How can we help?

You can also find more resources in our Help Center.

823 terms

MCAT Biology w/ Hormones

Review biology terms and hormones
STUDY
PLAY
5' cap
a methylated guanine nucleotide added to the 5' end of eukaryotic mRNA. The cap is necessary to initiate translation of mRNA
A band
The band of the sarcomere that extends the full length of the thick filament. The A band includes regions of thick and thin filament overlap, as well as a region of thick filament only. A bands alternate with I bands to give skeletal and cardiac muscle a striated apperance. The A band does not shorten during muscle contraction.
Absolute refractory period
A period of time following an action potential during which no additional action potential can be evoked regardless of the level of stimulation. (usually because Na+ channel closed whle K+ efflux)
Accessory glands
The three glands in the male reproductive system that reproduce semen: the seminal vesicles, the prostate, and the
Accessory organs
(1) In the GI tract, organs that play a role in digestion but not directly part of the alimentary canal. These include the liver, the gallbladder, the pancreas, adn the salivary glands.
Acetylcholine (Ach)
The neurotransmitter used throughout the parasympathetic nervous system as well as the neuromuscular junction.
Acetylcholinesterase (AChE)
The enzyme that breaks down acetylcholine in the synaptic cleft.
Acetyl-CoA
The first substrate in teh Krebs cycle, produced primarily from the oxidation of pyruvate by the pyruvate dehydrogenase complex, however acetyl-CoA is also produced during fatty acid oxidation and protein catabolism.
Acid hydrolases
Enzymes that degrade various macromolecules and that require an acidic pH to function properly. Acid hydrolases are found within the lysosomes of cells.
Acinar cells
Cells that make up exocrine galnds, adn that secrete their products into ducts. For example, in the pancreas, acinar cells secrete digestive enzyme; in the salivary glands, acinar cells secrete saliva.
Acrosome
A region at the head of a sperm cell that contains digestive enzyems which, when released during the acrosome reaction, can facilitate penetration of the corona radiata of the egg, and subsequently, fertilization
Actin
A contractile protein. In skeletal and cardiac muscle, actin polymerizes (along with other proteins) to form the thin filaments. Actin is involved in many contractile activities, such as cyotkinesis, pseudopod formation, and muscle contraction.
Action potential
A localized change in a neruon's or musce cell's membrane potential that can propogate itself away from its point of origin. Action potentials are an all-or-none process mediated by the opening of voltage-gated Na+ and K+ channels when the membrane is brought to the threshold potential; opening of the Na+ channels causes a characteristic depolarization, while opening of the K+ channels repolarizes the membrane.
Activation energy (Ea)
The amount of energy required to produce the transition state of a chemical reaction. If the activation energy for a reaction is very high, the reaction occurs very slowly. Enzymes (and other catalysts) increase reaction rates by reducing activation energy.
Active site
The 3D site of an enzyme where substrates (reactants) bind and a chemical reaction is facilitated.
Active transport
The movement of molecules through the plasma membrane against their concentration gradients. Active transport requires input of cellular energy, often in the form of ATP. An example is the Na+/K+ ATPase in the plasma membrane of all cells.
Adenine
One of the four aromatic bases found in DNA and RNA; also a component of ATP, NADH, and FADH2. Adenine is apurine; it pairs with thymine (in DNA) and with uracil (in RNA)
Adenohypophis
anterior pituitary gland
Adipocyte
fat cell
Adrenal medulla
The inner region of the adrenal gland. The adrenal medulla is part of the sympathetic nervous systme, and releases epinephrine (adrenaline) and norepinephrine into the blood when stimuated. These hormones augment and prolon the effects of sympathetic stimulation in the body.
Adrenergic tone
A constant input to the arteries that keeps them somewhat constricted to maintain a basal level of blood pressure.
Adrenocoricotropic hormone (ACTH)
A trop hormone produced by the anterior pituitary gand that targets the adrenal cortex, stimulating it to relase corisol and aldosterone.
Afferent arteriole
The small artery that carries blood toward the capillaries of the glomerulus.
Afferent neuron
A neuron that arries information (action potentials) to the central nervous system; a sensory neuron.
Albumin
A blood protein produced by the liver. Albumin helps to mantain blood osmotic pressure (oncotic pressure)
Aldosterone
The principal mineralocorticoid secreted by teh adrenal cortex. This steroid hormone targets the kidney tubules and increases renal reabsorption of sodium [and excretion of potassium]. (this causes ADH to be secreted & increased water comes out, increasing blood pressure indirectly).
Alimentary canal
Also known as the gastrointestinal (GI) tract of the digestive tract, the alimentary canal is the long muscular "tube" that includes the mouth esophagus, somatch, small intesitne, and large intestine.
Allosteric regulation
The modifaction of enzyme activity through interactino of molecules with specific sites on the enzyme other than the active site (called allosteric sites)
Alveoli
(singular alveolus.) Tiny sacs, with walls only a single cell layer thick found at the end of the respiratory bronchiole tree. Alveoli are the site of gas exchange in the respiratory system.
Allele
A version of a gene. For example, the gene may be for eye color, and the allels include those for brown eyes, those for blu e eyes, those green eyes, etc. At most, dploid organsims can posses only two alleles for a given gene, one on each of the two homologous chromosomes.
Amino Acid
The monomer of a protein; amino acids hae an amio group on one end fo the molecule and a carboxylic acid group on the other, and of the of 2 different side chains.
Amino acid acceptor site
The 3' end of a tRNA molecule that binds an amino acid. The nucleotide sequence at this end is CCA
Aminoacyl tRNA
A tRNA with an amino acid attached. This is made by an animoacyl-tRNA synthetase specific to the amino acid being attache.d
Aminion
A sac filled with fluid (aminotic fluid) that surroudns and protects a developing embryo.
Amphipathic
The characteristics of amolecule that has both polar (hydrophilic) and non-polar hydrophobic) regions, e.g. phospholipids, bile, etc.
Amylase
An enzyme that digests starch into disaccharides. Amylase is secreted by salivary glands and by the pancreas.
Anabolism
The process of bulidng complex structures out of simpler precursors, e.g. synthesizing protiens from amino acids.
Analogous structures
Physical structures in two different organism that have funcitonal similarity due to their evoluntion in a common environment, but have different underlying structure. Analogous structures arise from convergent evolution.
Anal sphincter
The valve that controls the release of feces from the recturm. It has an internal part made of smooth muscle (thus involuntary) and an external part made of skeletal muscle (thus voluntary).
Anaphase
The third phase of mitosis. During anaphase, replicated chromosmes are split apart at their centromeres (the sister chromatids are separated from each other) and moved to opposite sides of the cell.
Anaphase I
The third phase of meiosis I. During anaphase I the rplicated homologous chromosomes are separated (the tetrad is split) and pulled to opposite sides of the cell.
Anaphase II
The third phase of meiosis II. During anaphase II the sister chromatids are finally spearated at their centromeres and puled to opposite sides of teh cell. Note that anaphase II is identical to mitotic anaphase, excep the number of chromosmes was reduced by half during meiosis I.
Androgens
Mal sex hormones. Testosteron is the primary androgen.
Angiotensin
A normal blood protein produced by the liver, angiotensin is converted to angiotensim I by renin (secreted by kidney when blood pressur falls). Angiotensin I si further onverted to angiotensim II by ACE (angiotensin converting enzyme). Angiotensin II is a powerful systemic vasocontrictor ans stimulator of aldosterone relase, both of which result in an increase in blood pressure.
Antagonist
Something that acts to oppose the action of something else. For example, muscles that move a join in oppoiste direction are said to be antagonists.
Anterioir pituitary gland
Also known as the adenohypophysis, the anterior pituitary is made of gland tissue and makes and secretes six different homrones: FSH, LH, ACTH, prolactin, TSH, and growth hormone. The anterior pituitary is controlled b yreleasing and inhibiting factors from the hypothalamus.
Antibody (Ab)
Also called immunoblobins, the antibodies are protiens secreted by B-cells upon activation that bind in a highly specific manner to foreign proteins (such as those found of the surface of pathogens or transplanted tissues). The foreign proteins are called antigens. Antibodies generally do not directly destroy antigens, rather they mark them for destruction through other methods, and can inativate antigens by clumping them together or by convering necessary active sites.
Anticodon
A sequence of three nucleotides (found int he anticodon loop of tRNA) that is complementary to a specific codon in mRNA. The codon to which the anticodon is complementary specifies the amino acid that is carried by that tRNA.
Antidiuretic hormone (ADH)
Also called vasopressin, this hormone is produced in the hypothalamus and secreted by teh posterior pituitary gland. It tartes teh kidney tubules, increasing their permeability to water, adn thus increasing water retention by the body. Also raises blood pressure by inducing moderate vasoconstriction.
Antigen (Ag)
A molecule (usually a protein) capable of initiating an immune repsonse (antibody production).
Antigen presenting cell
Cells that possess MHC II (B cells and macrophages) and are able to display bits of ingested antigen on their surface in order to activate T cells. See also "MHC"
Antiparallel orientation
The normal configuration of double-stranded DNA in which the 5' end of oen strand is paired with the 3' end of the other
Antiporter
A carrier protein that transports two molecules acrss the plasma membrane in opposite directions.
Aorta
The largest artery in teh body; the aorta carries oxygenated blood away from the left ventricle of the heart.
Appendix
A mass of lymphatic tissue at the befenning of the large intestine that helps trap ingested pathogens.
Aqueous humor
A thin, watery fluid found in teh anterior segment of the eye (between the lens and the cornea). THe aqueous humor is constantly produced and drained, adn helps to bring nutrients to the lesn and corena, as well as to remove metabolic wastes
Arousal
A function in the reproductive system, controlled by the parasympathetic nervous system, that includes erection (via dilation of erectile arteries) and lubrication.
Artery
A blood vessel that carries blood away from the heart chambers. Arteries have muscular walls to regulate blood flow and are typically high-pressure vessles.
A site
Amino-acyl tRNA site; the site on a ribosome where a new amino acid is added to a growing peptide.
ATP synthase
A protein complex foudn in the inner membrane of the mitochondira. It is essentially a channel that llows H+ ions to flow from teh intermembrane space to the matrix (down teh gradeint produced by the enyzmes complexes of the electron transport chain); as the H= ions flow through the channel, ATP is synthesized from ADP and Pi
Atrioventricular bundle (AV) bundle
Also known as the Bundle of His, this is the first portion of the cardiac conduction system, after the AV node.
Atrioventricular (AV) node
The second major node of the cardiac conduction system (after the SA node). The cardiac impulse is delayed slightly at teh AV node, allowing the ventricles to contract just after the atria contract.
Atrioventricular valves
The valves in the heart that separte the atria from teh ventricles. The tricuspid valve separates teh right atrium from the right ventricel, and the bicuspid (mitral) valves separates the left atrium from the left ventricle. These valves close at the beginning of systole, preventing the backflow of bloo dfrom ventricles to atria, and producing the first heart sound (lub).
Atrium
One of the two small chambers in the heart that receive blood and pass it on to the ventricles. The right atrium receives deoxygenated blood from teh body through the superior and inferiro vena cavae, adn the left atrium receives oxygenated blood from teh lungs through the pulmonary veins.
Attachment
The first step in viral infection. Attachemen of a virus to its host is very specific and is also known as adsorption.
Auditory tube
The tube that connects the middle ear acity with the pharynx; also known as the Eustachian tube. Its fucntion is to equalize midle ear pressure with atmospheric pressure so that pressure on boths sides of the tympanic membrane is the same.
Autoimmune reaction
An immune reaction directed against normal (necessary ) cells.Fo example, diabets melitus (typeI) is an autoimmun reaction directed against teh beta cells of the pancrease (destorying them and preventing insulin secretion) and aginst insulin itself.
Autonomic nervous system (ANS)
The division of the periperal nervsous system that innervates and cotnrols the visceral organs (everything but the skeletal muscles). It is also knowns as the involuntary nervous system and an be subdivided into the sympathetic and parasympathetic divisions.
Autosome
A chromosome that does not determine gender (is not a sex chromosome). Humans have two sex chromsomes and 22 autosomes.
Autotroph
An organism that makes its own, typically using CO2 as a carbon source.
Auxotroph
A bacterium that cannon survive on minimal medium (glucose alone) because it lacks the ability to syntheisze a molecule it needs to live (typically an amino acid). Auxotrphs must ave the needed substance (the auxiliary trophic substance) added to their medium in order to survive. The are typically denoted by teh susbstance they require followed by a "-" sign in superscript. For example, a bacterium that cannot syntehisze leucine would be a leucine auxotroph, and would be indicated as leu- (w/ a superscripth, though)
Avascular
Lacking a blood supply; cartialge is an example of this
Axon
A long projection off the cell body of a neruon down which an action potential can be propagated.
Bacilus
A bacterium having a rod-like shaped (plural = bacilli).
Bacteriophage
A virus that infects a bacterium.
Baroreceptor
A sensory receptor that responds to hcanges in pressure; for example, there are baroreceptors in the carotid arteries and the aortic ach that monitor blood pressure.
Basement membrane
A layer of collagen fibers that separates epithelial tissue from connective tisse (example of epithelial cells in digestive tract) - they are actual connective tissue.
Basilar membrane
The flexible membrane in teh chochlea that supports the organ of Corti (structure which contains the hearing receptors). The fibers of the basilar membrane are short and stiff near the oval windown and long and fleaxible near the apex of the cochlea. This difference in structure allows the basilar membrane to help trasnduce pitch.
B cell
A type of lymphocyte that can recognize (bind to) an antigen adn secrete an antibody specific for that antigen. When activated by binding an antigen, B cells mature into plasma cells (that secreted antibody) and memory cells (that patrol the body for future encounters with that antigen). - must be activated by Helper T cell also, though.
Bicarbonate
HCO3-. THis ion results from the dissociation of carbonic acid, together wiht carbonic acid forms the the major blood buffer system. Bicarbonate is also secreted by teh pancreas to neutralize stomach acid in the intestines.
Bile
A green fluid made from cholesterol and secreted by teh liver. It is stored and concentrated in the gallbladder. Bile isn an amphipathic molecule that is secreted itno the small intestine when fats are present, adn serves to emulsify the fats for better digestion by lipases.
Binary fission
An asexual method of bacterial reproduction that serves only to increase the size of the population; ther is no introduciton of gnetic diversity. THe bacterium simply grows in size until it has doubled its cellular components, then it replicates its genone and splits into two.
Bipolar neuron
A neuron with a single axon and a single dendrite, often projecting from opposite sides of the cell body. Bipolar neurons are typically associated with sensory organs; an example is the bipolar neuron in the retina of the eye. - note that one axon may innervate many different muscles, or other things.
Blastocyst
A fluid-filled sphere formed about 5 days after fertilization of an ovum that is made up of an outer ring of cells and inner cell mass. THis is the structure that implants in the endometrium of the uterus.
Bohr effect
The tendency of certain factors to stablize the hemoglobin in the tense conformation, thus reducing its affinity for oxygen and enhancing the relase of oxygen to the tissues. The factors include increased PCO2, increase temperature, increased bisphosphoglycerate (BPG), and decreased pH. Note that the Bohr effect shifts the oxy-hemolobin saturation curve to the right.
Bone marrow
A non-bony material that fills the hollow spaces inside bones. Red bone marrow is found in regiosn of spongy bone and is the site of blood cell (red and white) production. Yellow bone marrow is found in the diaphysis (shaft) of long bones, is mostly flat, and is inactive.
Bowman's capsule
The region of the nephron that surrounds the glomerulus. The capsule ollects the plasma that is filtered from teh capillaries in the glomerulus.
Bronchioles
Very small air tubes int eh respiratory system (diameter 0.5 - 1.0 mm). The walls of the bronchioles are made of smooth muscle (thus involunatry) to help regulate air flow.
Brush border enzymes
Enzymes secreted by the mucosal cells lining the intestine. The brush border enzymes are disaccharides adn dipeptidases taht digest the smallest peptides and carbohydrates into their respective monomers.
Bulbourethral galnds
Small paired gland found inferior to the prostate in males and at the posterior end of the penile urethra. They secrete an alkaline mucus on sexual arousal that helps toneutralize any traces of acidic urine the urethra that might be harmful to sperm.
Calcitonin
A hormone produced by the C-cells of the thyroid gland that decreases serum calcium levels. It targets teh bones (stimulates osteoblasts), the kidneys (reduces calcium reabsorption), and the small intestine (decreases calcium absorption).
Calcitriol
A hormone produced from vitamin D that acts in essentially the same manner as parathyroid hormone.
Calmodulin
A cyoplasmic Ca2+-binding protein. Calmodulin is particularly important in smooth muscle cells, where binding of Ca2+ allows calmodulin to activate myosin light-chian kinase, the first step in smooth muscle cell contraction.
Canaliculus
Very small tube or channel, such as is found between lacunae (connecting them together) in compact bone.
Capacitation
An incrase in the fragility of the membranes of sperm cells when exposed to the female reproductive tract. Capacitation is required sot aht the acrosomal enzymes can be relased to faciliate fertilization.
Capilary
The smalles of all blodo vessles, typically having a diamtere just large neough for blood cells to pass through in single file. Capillaries have extremelyu thin walls to faciliate the exchange of material between the blood and the tissues.
Capsid
The outer protein coat of a virus (the whole coat)
Carbohydrates
Molecules made from monosaccharides that serve as the primary source of cellular energy,. Carbohydrates can also act as cell surface markers (good thing to remember).
Carbonic anhydrase
An enzyme present in erythrocytes (as well as in other places) that catalyzes the conversion of CO2 and H2O into carbonic acid (H2CO3).
Cardiac conduction system
The specialized cells of the heart that spontaneously initiate action potentials and transmit them to the cardiac muscle cells. The cells of the conduction system are essentially cardiac muscle cells, but lack the contractile fibers of the muscle cells, tus they are able to transmit impulses (action ptnetials) more quickly and efficiently that cardiac muscle tissue. The cardiac conduction system includes the SA node, the internodal tract, he Av node, the AV bundle, the right and left bundle branches, and the Purkinje fibers.
Cardiac muscle
The muscle tissue of the heart Cardiac muscle is striated, uninucleate, and under involuntary control (controlled by teh autonomic nervous system). Note also that cardiac muscle is self-stimulatory, and autonomic control serves only to modify the intrinsic rate of contraction.
Cardiac output
The volume of blood pumped out of the heart in one minute (vol/min); the product of the stroke volume (vol/beat) and the heart rate (beat/min). Cardiac output is directly proportional to blood pressure**.
Carrier protein
An integral membrane protein that undergoes a conformational change to move a molecule from one side of the membrane to another. See also 'uniporter', 'antiporter', and 'symporter'.
Cartilage
A strong connective tissue with varying degrees of flexibility. (1) Elastic cartilage is the most flexible, forming structures that reuqire support but also need to bend, such as the epiglottis and outer ear. (2) Hyaline cartilage is more rigid than elastic cartilage, and forms the cartilages of the ribs, the respiratory tract, and all joints. (3) Fibrocartilage is the least flexible of them all, and forms very strong connections, such as the public symphysis and the intervertebral disks.
Catabolism
The process of breaking down large molecules into smaller precursors, e.g. digesion of starch into glucose.
Catalase
The primary enzyme in peroxisomes; catalse catalyzes the hydrolysis of hydrogen peroxide (H2O2) into water and oxygen.
Catalyst
Something that increases the rate of a chemical reaction by reducing the activation energy for that reaction. The free energy of reaction remains unchanged.
cDNA
Complementary DNA. DNA produced synthetically by reverse trascribing mRNA. Because of eukaryotic mRNA splicing, cDNA contains no inrons.
Cecum
The first part of the large intestine.
Cell surface receptor
An integral membrane proteint hat binds extracellular signaling molecules, suchas hormones and peptides.
Central canal
The hollow center of an osteon, also known as a Haversian canal. The central canal contains blood vessels, lymphatic vessels, lymphatic vessels, and nerves. Bone is laid down around the central canal in concentric rings called lamellae.
Central chemoreceptors
Receptors in the central nervous system that monitor the pH of cerebrospinal luid to help regulate ventilation rate.
Central Nervous System
The subdivision of the nervous system consisting of the brain and spinal cord.
Centriole
A structure composed of a ring of nine microtube triplets, found in pairs in the MTOC (microtubule organizing center) of a cell. The centrioles duplicate during the cell division, and serve as the organizing center for the mitotic spindle.
Centromere
A structure near the middle of eukaryotic chromosomes to which the fibers of the mitotic spindle attach during cell division.
Cerebellum
The region of teh brain that coordinates and smooth skeletal muscle activity.
Cerebral cortex
A thin (4 mm) layer of gray matter on the surface of the cerebral hemispheres. The cerebral cortex is the conscious mind, and is functionally divided into four pairs of lobes: the frontal lobes, the parietal lobes, the temporal lobes, and the occipital lobes.
Cerebrospinal fluid
A clear fluid the circulates around through the brain and spinal cord that helps to physially support teh brain and act as a shock absorber, and taht also exchanges nutrients and wastes with teh brain and spinal cord.
Ceruminous gland
A gland that secretes a waxy product, found in the external ear canal.
Cervix
The opening to the uterus The ervix is typically plugged with a sticky acidic mucus during non-fertile times (to form a barrier against the entry of pathogens), however during ovulation the mucus becomes more watery and alkaline to facilitate sperm entry.
Channel protein
An integral protein that selectively allows molecules across the plasma membrane. See also entries under 'ion channel', 'voltage-gated channel', and 'ligand-gated channel'.
Chemical synapse
A type of synapse at which a chemical (a neurotransmitter) is released from teh axon of a neuron into the ysnaptic cleft where it binds to receptors on the next structure in sequence, either another neuron or an organ.
Chemoreceptor
A sensory receptor that responds to specific chemicals. Some examples are gustatory (taste) receptors, olfactory (smell) receptors, and central chemoreceptors (responds to pH changes in teh cerebrospinal fluid).
Chemotaxis
Movement that is directed by chemical gradients, such as nutrients or toxins. (seen in some bacteria)
Chemotroph
An organism that relies on a chemical source of energy (such as ATP) instead of light (which phototrophs).
Chief cells
Pepsinogen-secreting cells foudn at teh bottom of the gastric glands
Chitin
A poysaccharide found in the cell walls of fungi and in the exoskeletons of insects.
Cholecystokinin (CCK)
A hormone secreted by the samll intestine (duodenum) in response to the presence of fats. It promotes release of bile from the gallbladder and pancreatic juice from the pancreas,and reduces stomach motility.
Cholesterol
A large, ring shaped lipid found in cell membranes. Cholesterol is the precursor for steroid hormones, and is used to manufacture bile salts.
Chondrocyte
A mature, cartilage cell.
Chorion
The portion of the placenta derived from the zygote.
Choroid
The darkly pigmented middle layer of the eyeball, found between teh sclera (outer layer) and the retina (inner layer).
Chromosome
A single piece of double-stranded DNA; part of the genome of an organism. Prokaryotes have circular chromosomes and eukaryotes have linear chromosomes.
Chylomicron
A type of lipoprotein; the form in which absorbed fats from the intestines are transported to the circulatory system.
Chyme
Partially digested, semiliquid food mixed with digestive enzymes and acids in the stomach.
Chymotrypsin
One of the main pancreatic proteases; it is activated (from chymotrypsinogen) by trypsin.
Cilia
A hair-like structure on teh cell surface composed of microtubules ina '9+2' arrangement (nine pairs of microtubles surrounding 2 single microtubules in the center). Teh microtubules are conneted with a contractile protien called dynein. Cilia beat in a repetitive sweeping motion, which helps to move substances along the surface of the cell. They are particularly important in the respiratory system, where they sweep mucus out of the trachea and up to the mouth and nose.
Ciliary muscles
Muscles that help focus light on teh retin by controlling the curvature of the lens of the eye.
Circular smooth muscles
The inner layer of smooth muscle in the wall of the digestive tract. When the circular muscle contracts, the tube diameter is reduced. Certain areas of the circular muscle are thickened to act as valves (sphincters).
Clathrin
A fibrous protein found on the intracellular side of the plasma membrane (also associated with the Golgi complex) that helps invaginate the membrane. Typically cel surface receptors are associated with clathrin-coated pits at the plasma membrane binding of the ligan to the receptor trigger invagination (example: cholesterol uptake via lipoprotein endocytosis).
Cleavage
The rapid mitotic division of a zygot that being within 24-36 hours after fertilization
Coccus
A bacteria having a round shape (plural = cocci)
Cochlea
The curled structure in the inner ear that contains the membranes and hair cells that transduce sound waves into action potentials.
Codominance
A situation in which a heterozygote displays the phenotype associated with each of the alleles, e.g., human blood type AB.
Codon
A group of three nucleotides taht is specific for a particular amino acid, or that specifies 'stop translating'
Coenzyme
An **organic molecuel taht associates non-covalently with an enzyme, and that is required for the proper functioning of the enzyme.
Cofactor
An **inorganic molecule that associates non-covalently with an enzyme and that is required for the proper functioning of the enzyme
Collagen
A protein fiber with a unique triple-helix that gives it great strength. Tissues with a lot of collagen fibers are typically very strong, e.g. bone, tendons, ligaments, etc.
Collecting duct
The portion of the nephron where water reabsorption is regulated via antidiuretic hormone (ADH). Several nephrons empty into each collecting duct, and this is the final region through which urine must passon its way to the ureter.
Common bile duct
The duct that carries bile from the gallbladder and liver to the small intestine (duodenum).
Compact bone
A dense, hard type of bone constructed from osteons (at the microscopic level). Compact bone forms the diaphysis of the the long bones, and the outer shell of the epiphyses and all other bones.
Competitive inhibitor
An enzyme inhibitor that competes with substrate for binding at the active site of teh enzyme. When the inhibitor is bound, no product can be made.
Complement system
A group of blood proteins that bind non-specifically to the surface proteins of foreign cells (such as bacteria), ultimately leading to the destruction of the foreign cell - part of the innate immunity.
Cones
Photoreceptors in the retina of the eye that responds to bright light and provide color vision.
Conjugation
A form of genetic recombination in bacteria in which plasmid and/or genomic DNA is transferred from one bacterium to the toher through a conjugation bridge.
Connective tissue
One of the four basic tissue types in the body (epithelial, connective, muscle, and nervous). Connective tissue is a supportive tissue consisting of a relatively few cells scattered among a great deal of extracellular material (matrix), and includes adipose tissue (fat), bone, cartilage, the dermis of teh skin, tendons, ligaments, and blood.
Convergent evolution
A form of evolution in which different organisms are placed into the same environment and exposed to teh same selection pressures. This causes the organisms to evolve along similar lines. As a result, they may share functional, but not structural similarity (because they possessed different startgin materials). Convergent evolution produces analogous structures.
Cooperativity
A type of substrate binding to a multi-active site enzyme, in which the bnidng of one substrate molecule facilitates teh binding of subsequent substrate molecules. A graph of reaction rate vs. substrate concentration appears sigmoidal. Noe that cooperativity can be foudn in other situations as well, for example, hemoglobin bind oxygen cooperatively.
Cornea
The clear portion of the tough outer layer of teh eye ball, found over the iris and pupil
Corona radiata
The layer of granulosa cells taht surround an oocyte after is has been ovulated.
Coronary vessels
The blood vessels taht carry blood to and from cardiac muscle. The coronary arteries branch off teh aorta and carry oxygenated blood to the cardiac tissue. The coronary veins collect deoxygenated blood from teh cardiac tissue, merge to form teh coronary sinus, and drain into the right atrium.
Corpus callosum
The largest bundle of white matter (axons) connecting th two cerebral hemispheres.
Corpus luteum
'Yellow body.' The remnants of an ovarian follicle after ovulation has occurred. The cells enlarge and begin secreting progesterone, the dominant female hormone during the second half of the menstrual cycle. Some estrogen is also secreted.
Cortex
The outer layer of an organ, e.g. the renal cortex, the ovarian cortex, the adrenal cortex, etc.
Corticosteroids
Steroid hormones secreted from the adrenal cortex. The two major classes are teh mineralocorticoids and glucocorticoids. Aldosterone is the principal mineralocorticoid, and cortisol is the principal glucorcorticoid.
Cortisol
The principal glucocorticoid secreted from teh adrenal cortex. This steroid hormone is released ruing stress, causing increased blood glucose levels and reducing inflammation. The latter effect has led to a clinical use of cortisol as an anti-inflammatory agent.
Creatine Phosphate
An energy storage molecule used by muscle tissue. The phosphate from creatine phosphate can be removed and attached to an ADP to generate ATP quickly.
Cristae
The folds of the inner membrane of a mitochondrion
Cross bridge
The connection of a mosin head group to an actin filament during muscle contraction (the sliding filament theory).
Crossing over
The exchange of DNA between paired homologus chromosomes (tetrads) during prophase I of meiosis.
Cyclic AMP (cAMP)
A cyclic version of adenosine monophosphate, where the phosphate is esterified to both the 5' and 3' carbons, forming a ring. Cyclic AMP is an important intracellular signaling moelcule, often called the 'second messenger.' It serves to activate cAMP-dependent kinases, which regulates the activity of other enzymes in the cell. Levels of cAMP are in part regulated by adenylyl cyclase, the enzyme that makes cAMP, adn the activity of adenylyl cyclase i ultimately controlled by the binding of various ligands to cell surface receptors.
Cytokinesis
The phase of mitosis during which the cell physically splits into two daugter cells. Cytokinesis begins near the end of anaphase, and is completed during telophase.
Cytosine
One of the four aromatic bases found in DNA and RNA. Cytosine is a pyrimidine; it pairs with guanine.
Dendrite
A projection of the cell body of a neuron that recieves a nerve impulse form a different neuron and send the impulse to the cell body. Neurons can have one or several dendrites!
Dense connective tissue
Connective tissue with large amounts of either collagen fibers (making them strong) or elastic fibers, or both. Dense tissues are typically strong (e.g. bone, cartilage, tendons, etc.)
Depolarization
The movement of teh membrane potential of a cell away from rest potential in a more positive direction.
Dermis
A layer of connective tissue underneath the epidermis of the skin. The dermis contains blood vessels, lymphatic vessels, nerves, sensory receptors, and glands.
Desmosome
A general cell junction, used primarily for adhesion.
Determination
The point during development at which a cell becomes committed to a particular fate (sensory, other, etc.). Note that the cell is not differentiated at this point; determination comes before differentiation. Determination can be due to cytoplasmic effects or to induction by neighboring cells.
Diaphragm
The primary muscle of inspiration. The diaphragm is stimulated to contract at regular intervals by the respiratory center in the medulla oblongata (via the phrenic nerve). Although it is made of skeletal muscle (and can therefore be voluntary controlled), these stimulations occur autonomously.
Diaphysis
The shaft of a long bone. The diaphysis is hollow and is made entirely from compact bone.
Diastole
The perio of time during which the ventricles of the heart are relaxed.
Diastolic pressure
The pressure measured in the arteries while the ventricles are relaxed (during diastole).
Diencephalon
The portion of theforebrain that includes the thalamus and hypothalamus.
Differentiation
The specialization of cell types, especially during the embryonic and fetal development.
Diffusion
The movement of a particle (the solute) in a solution from its region of high concentration to its region of low concentration ( or down it concentration gradient).
Diploid organism
An organism that has two copies of its genome it each cell. The paired genomes are said to be homologous.
Disaccharide
A molecule composed of two monosaccharides. Common disaccharides include maltose, sucrose, and lactose.
Distal convoluted tubule
The portion of the nephron tubule after the loop of Henle, but before teh collecting duct. Selective reabsorption and secretion occur here, most notably regulated reabsorption of water and sodium.
Divergent evolution
A form of evolution in which the same organism is placed into different environments with different selection pressures. This causes organisms to evolve differently, to diverge from their common ancestor. The resulting (new) species may share structural (but not necessarily functional) similarity; divergent evolution produces homologous structures.
DNA polymerase
Also called DNA pol, this is the enzyme that replicates DNA. Eukaryotes have a single version of the enzyme, simply called DNA pol (not need to know much detail); prokaryotes have three versions, called DNA pol I, DNA pol II, and DNA pol III.
Dominant
The allele in a heterozygous genotype that is expressed; the phenotype resulting from either a heterozygous genotype or a homozygous dominant genotype.
Dorsal root ganglion
A group of sensory neuron cell bodies found just posterior to the spinal cord on either side. A pair of root ganglia exists for each spinal nerve that expands from the spinal cord. The ganglia are part of the peripheral nervous system (PNS).
Downstream
Toward the 3' end of an RNA transcript (the 3' end of the DNA coding strand). Stop codons and (in eukaryotes) the pol-A tail are found 'downstream.'
Duodenum
The first (approximately 5%) of the small intestinte.
Dynein
A contractile protein connecting microtubules in the '9+2- arrangement of cilia and eukaryotic flagella. The contraction of dynein produces the characteristic movement of these structures.
Ectoderm
One of the three primary (embryonic) germ layers formed during gastrulation. Ectoderm ultimately forms external structures such as the skin, hair, nails, and inner linings of the mouth and anus, as well as the entire nervous system.
Edema
Swelling of tissues, sometimes caused by inflammation letting into many white blood cells (decreasing oncotic pressure at the end of the capillaries & not letting as much water back into capillaries & staying in tissues).
Effector organ
The organ that carries out teh command sent along a particular motor neuron
Efferent arteriole
The small artery that carries blood away from the capillaries of the glomerulus.
Efferent neuron
A neuron that carries information (action potentials) away from the central nervous system; a motor neuron.
Ejaculation
A subphase of male orgasm, a reflex reaction triggered by the presence of semen in the urethra. Ejaculation is a series of rhythmic contractions of muscles near teh base of teh penis that increase pressure in the urethra, forcing the semen out.
Ejection fraction
The fraction of teh end-diastolic volume ejected from the ventricles in a single contraction of teh heart. THe ejection fraction is normally around 60% of the end diastolic volume.
Elastin
A fibrous, connective-tissue protein taht has the ability to recoil to its original shape after being stretche.d Elastin is found in great amounts in lung tissue, arterial tissue, skin, and the epiglottis.
Electrical synapse
A type of syanpse in which the cells are connected by gap junctions, allowing ions (and therefore an action potential) to spread easily from cell to cell, usually in smooth and cardiac muscle. - compared to chemical synapse.
Electron transport chain
A series of enzyme complexes found along the inner mitochondrial membrane. NADH and FADH2 are oxidized by tehse enzymes; the electrons are shuttled down the chain and are ultimately passed to oxygen and to produce water. The electron energy is used to pump H+ out of the mitochondrial membrane; the resulting H+ gradient is subsequently used to drive the production of ATP.
Embryonic stage
The period of human development from implantation through 8 weeks of gestation. Gastrulation, neurulation, and organogenesis occur during this time period. The developing baby is known as embryo during this time period.
Emission
A subphase of male orgasm. Emission is the movement of sperm (via the vas deferens) and semen into the urtehra in prepartion for ejaculation.
Endocrine gland
A ductless gland that secretes a hormone into the blood
Endocrine system
A systme of ductless glands taht secrete chemical messengers (into) the blood - has to be into the blood.
Endocytosis
The uptake of material into a cell, usually by invagination. See also 'phagocytosis', pinocytosis, and receptor-mediated endocytosis..
Endoderm
One of the three primary (embryonic) germ layers formed during gastrulation. Endoderm ultimately forms internal structures, such as the inner lining of the GI tract and glandular organs.
Endometrial cycle
The 28 days of the menstrual cycle as they apply to the events in the uterus. The endometrial cycle is also known as the uterine cycle, and has the three subphases: menstruation, the proliferative phase, and the secretory phase.
Endometrium
The inner epithelial lining of the uterus that thickens and develops during the menstrual cycle, into which a fertilized ovum can implant, and which sloughs off during menstration if a pregnancy does not occur.
Endospore
A bacterial structure formed in unfavorable growth conditions. Endospores have very rough outer shells made of peptidoglycan and can survive harsh conditions. The bacterium inside the endospore is essentially dormant and can become active (called germination) when conditions again become favorable.
Endosymbitoic theory
the theory that mitochondria and chloroplasts originated as independent unicellular organsims living in symbiosis with larger cells
Endotoxin
A normal component of the outer membrane of Gram-negative bacteria. Endotoxins produce extreme immune reactions (septic shock), particularly when many of them enter the circulation at once.
End plate potential
The depolarzation of the motor end plate on a muscle cell.
Enteric nervous system
The nervous system of the gastrointestinal tract. It controls secretion and motility within teh Gi tract, and is linked to the central nervous system.
Enterogasterone
A hormone secreted by the small intestine (duodenum) in response to the presence of food. It decreases the rate at which chyme leaves the stomach and enters the small intestine.
Enterokinase
A duodenal enzyme that activates trypsinogen (from the pancreas) to trypsin.
Envelope
A lipid bilayer that surrounds the capsid of an animal virus. the envelope is acquired as teh virus buds out through the plasma membrane of its host cell. Not all annimal viruses possess and envelope.
Enzyme
A physiological catalyst. Enzymes are usually proteins, although some RNAs have catalytic activity.
Epidermis
The outermost layer of teh skin. The epidermis is made of epithelial tissue that is constantly dividing at the bottom; teh cells migrate to teh surface (dying along the way) to be sloughed off at the suface.
Epididymis
A long, coiled duct on the outside of the testis in which sperm mature.
Epiglottis
A flexible piece of cartilage in the larynx that flips downward to seal teh trachea during swallowing.
Epinephrine
A hormone produced and secreted by teh adrenal medulla that prolongs and increases teh effects of the sympathetic nervous system.
Epiphyseal plate
A band of carilage (hyaline) found between the diaphysis and epiphyses of long bones during childhood and adolescence. Cell proliferation in the middle of the eiphyseal plate essentially forces teh diaphysis and epiphyses further apart, while the older cartilage at the endes of the plate is replaced with bone. This is waht allows bone growth during childhood. The epiphyseal plate gets thinner and thinner teh older a person gets, until finally it fuses ( the diaphysis and epiphyses connect) in late adolescence, preventing further elongation of teh bones.
Epiphysis
One of the two ends of long bone (pl: eiphyses). The epiphyses have an outer shell made of compact bone and inner core of spongy bone. The spongy bone is filled with red bone marrow, the stie of blood cell formation.
Epistasis
A situation in which the expression of one gene prevents expression of all allelic forms of another gene, e.g., the gene for male pattern baldness is epistatic to the hair color gene.
Epithelial tissue
One of the four basic tissue types in the body (epithelial, connective, muscle, and nervous). Epithelial tissue is a lining and covering tissue (e.g. skin, the lining of the stomach and intestines, the lining of the urinary tract, etc. ) or a glandular tissue (e.g. the liver, the pancreas, the ovaries, etc.)
Epitope
The specific site on an antigenic molecule that binds to a T cell receptor or to an antibody.
EPSP
Excitatory postsynaptic potential; a slight depolarization of a postsynaptic cell, bringing the membrane potential of that cell closer to the threshold for an action potential.
Erectile tissue
Specialized tissue with a lot of space that can fill with blood upon proper stimulation, causing teh tissue to become firm. Erectile tissue is found in the penis, the clitoris, the labia, and the nipples.
Erythrocyte
A red blood cell; they are filled with hemoglobin, and teh function of the erythrocytes is to carry oxygen in the blood.
Erythropoietin
A hormone produced and released by the kidney that stimulates the production of red blood cells by the bone marrow.
Estrogen
The primary female sex hormone. Estrogen stimulates the development of female secondary sex characteristics during puberty, maintains those characteristics during adulthood, stimulates the development of a new uterine lining after menstruation, and stimulates mammary gland development during pregnancy.
Euchromatin
DNA that is loosely packed around histones. This DNA is more accessible to enzymes and the genes in euchromatin can be activated if needed.
Eukaryotic
A cell characterized by the presence of a nucleus and other membrane-bound organelles. Eukaryotes can be unicellular (protists) or multicellular (fungi, plants and animals).
Exclusion
The removal ( and usually the activation) of a viral genome from its host's genome.
Excitation-contraction coupling
The mechanism that ensures tehat skeletal muscle contraction does not occur without neural stimulation (excitation). A trest, cytosolic [Calcium] is low, and the troponin, tropomyosin complex covers the myosin-binding sites on actin. When the muscle is stimulated by a neuron, calcium is released from the sarcoplasmic reticulum into teh cytosol of the muscle cell. Calcium binds to troponin, causing a conformation change in the troponin-tropomyosin complex that shifts it away from the myosin-binding sites. This allows mysoin and actin to interact according to the sliding filament theory.
Excretion
The elimination of wastes from the body.
Exocrine gland
A gland that secretes its product into a duct, which ultimately carries the product to the surface of the body or into a body cavity. Some examples of exocrine gland and their products are sweat glands (sweat), gastric glands (acid, mucus, protease), the liver (bile), sebaceous glands (oil), and lacrimanl glands (tears).
Exocytosis
The secretion of a cellular product to the extracellular medium through a secretory vesicle.
Exon
A nucleotide sequence in RNA that contains protein-coding information. Exons are typically separated by introns (intervening sequences) that are spliced out prior to translation.
Exotoxin
A toxin that secreted by a bacterium into its surrounding medium that help the bacterium compete with other species. Some exotoxins cause serious disease in humans (botulism, tetanus, diptheria, toxic shock syndrome).
Expiration
The movement of air out of the respiratory tract. Expiration can be passive (caused by relaxation of the diaphragm and elastic recoil of the lungs) or active (caused by contraction of the abdominal muscles, which increases intraabdominal pressure and forces the diaphragm up past its normal relaxed position).
Facilitated diffusion
Movement of a hydrophilic molecuel across the plasma membrane of a cell, down its concentration gradient, through a channel, pore, or carrier molecule in the membrane. Because the hydrophilic nature of the molecule, it requires a special path through the lipid bilayer.
Facultative anaerobe
An organism that will use oxygen (aerobic metabolism) if it is available, and that can ferment (anaerobic metabolism) if it is not.
FADH2
The reduced from (carries electrons) of FAD (flavin adenine dinucleotide). this is the other main electron carrier in cellular respiration (NADH is the most common).
Fascicle
A bundle of skeletal muscle cells. Fascicles group together to form skeletal muscles.
Fast block to polyspermy
The depolarization of the egg plasma membrane upon fertilization, designed to prevent the entry of more than one sperm into the egg.
Feedback inhibition
Also called negative feedback, the inhibition of an early step in a series of events by the product of a later step in the series. This has the effect of stopping the series of events when the products are plentiful and the series is unnecesseary. Feedback inhibition is the most common form of regulation in the body, controllin such things as enzyme reactions, hormone levels, blood pressure, body temperature, etc.
Fermentation
The reduction of pyruvate to either ethanol or lactate in order to regenerate NAD+ from NADH. Fermentation occurs in the absence of oxygen, and allow glycolysis to continue under those conditions.
Fertilization
The fusion of a sperm with an ovum during sexual reproduction. Fertilization typically occurs in the uterine tubes and requires capacitation of the sperm and relase of the acrosomal enzymes. Fertilization is a species-specific process, requiring binding of a sperm protein to an egg receptor.
F (fertility) factor
A bacterial extrachromosal elent that allows the bacterium to initati conjugation. Bacteria that possess teh F factor are known as F+ 'males'.
Fetal stage
The period of human development beginning at 8 weeks of gestation and lasting until birth (38-42 weeks of gestation). During this stage the organs formed in the embryonic stage grow and mature. The developing baby is known as a fetus during this time period.
Fibrinogen
A blood protein essential to blood clotting. The conversion of fibrinogen to its active form (fibrin) is among the final steps in clot formation, and is triggered by thrombin.
Fibroblast
A generic connective tissue cell that produces fibers; the progenitor of all other connective tissue cell types.
Filtration
The movement of a substance across a membane via pressure. In the kidney, filtration refers specifically to the movement of plasma across the capillary walls fo the glomerulus, into the capsule and tubule of the neprhon. Filtration at teh glomerulus is driven by flood pressure.
Fimbriae
Fingerlike projection of the uterin (fallopian) tubes that drape over the ovary.
First law of Thermodynamics
The law of conservation of energy; the energy of the universe is constant, thus if the energy of a system increases, the energy of its surroundings must decrease, and vice versa.
Flagella
A long, whip-like filament that helps in cell motility. Many bacteria are flagellated, and sperm are flagellated.
Fluid mosaic model
the current understanding of membrane structure, in which teh membrane iscomposed of a mix o lipids and proteins (a mosaic) that are free to move fluidly among themselves.
Follicle
A developing oocyte and all of its surrounding (supporting) cells.
FSH
A tropic hormone produced by the anterior pituitary gland that targets the gonads. In females, FSH stimulates the ovaries to develop follicles (oogenesis) and secrete estrogen; in males, FSH stimulates spermatogenesis.
Follicular phase
The first phase of the ovarian cycle, during which a follicle (an oocyte and its surroudning cells) enlarges and matures. This phase is under the control of FSH from the anterior pituitary, and typically lasts from day 1 to day 14 of the menstrual cycle. The follicle secretes estrogen during this time period.
F1 generation
The first generation of offspring from a given genetic cross.
Formed elements
The cellular elements of blood; erythrocytes, leukocytes, and platelets.
Frameshift mutation
A mutation caused by an insertion or deletion of base pairs in a gene sequence in DNA such that the reading frame of the gene (and thus teh amino acid sequence of the protein) is altered.
Frank Starling mechanism
A mechanism by which the stroke volume of the heart is increased by increasing the venous return of the heart (thus stretching the ventricular muscle).
Functional synctium
A tissue in which the cytoplasms of the cells are connected by gap junctions, allowing the cells to function as a unit. Cardiac and smooth muscle tissues are examples of functional synctiums.
Gallbladder
A digestive accessory organ near the liver. The gallbladder stores and concentrates bile produced by the liver, and is stimulated to contrat by cholecystokin (CCK).
Gametogenesis
The formation of haploid gametes (sperm or ova) via meiosis.
Ganglion
A clump of gray matter (unmyelinated neuron cell bodies) found in the peripheral nervous system.
Gap junction
A junction between cells, consisting of a protein channel called a connexon on each of the two cells that connect to form a single channel between teh cytoplasms of both cells. Gap junctions allow small molecules to flow between teh cells, and are important in cell-to-cell communication, for example, in relaying the action potential between cardiac muscle cells, and relaying nutrients between osteocytes.
Gap phase
A phase in the cycle between mitosis and S phase (G1) or between S phase and mitosis (G2). During gap phases the cell undergoes normal activity and growth; G1 may include preparation for DNA replication and G2 includes preparation for mitosis. Note that non-dividing cells remain permanently in G1, known as Go for these cells.
Gastrin
A hormone released by teh G cells of the stomach in the presence of food. Gastrin promotes muscular activity of the stomach as well as secretion of hydrochloric acid, pepsinogen, and mucus.
Gastrulation
the division of the inner cell mass of a blastocyst (developing embryo) into the three primary germ layers. Gastrulation occurs during weeks 2-4 of gestation.
Gene
A portion of DNA that codes for some product, usually a protein, including all regulatory sequences. Some genes code for rRNA and tRNA, which are not translated.
Gene pool
The sum of all genetic material in a population.
Genetic code
The 'language' of a molecular biology that specifies which amino acid corresponds to which three-nucleotide group (codon).
Genome
All the genetic information in an organism; all of an organism's chromosomes.
Genotype
The combination of alleles of an organism carries. In a homozygous genotype, both alleles are the same, whereas in a heterozygous gentorype the alleles are different.
Gibbs free energy
The energy in a system that can be used to drive chemical reactions. If the change in free energy of a reaction (Delta G, the free energy of the products minus the free energy of the energy of the reactants) is negative, the reaction will occur spontaneously.
Glomerulus
The ball of capillaries at the beginning of the nephron where blood filtration takes place.
Glucagon
A peptide hormone produced and secreted by the alpha cells, of the pancreas. It tartes primarily the liver, stimulating the breakdown of glycogen, thus increasing blood gluocse level.s
Glycolipid
A membrane lipid consisting of a glycerol molecule esteried to two fatty acid chains and a sugar molecule.
Goblet cells
Unicellular exocrine glands found along the respiratory and digestive tracts taht secrete mucus.
Golgi apparatus
A stack of membranes found near the rough ER in eukaryotic cells that is involved in the secretory pathway. The Golgi is involved in protein glycosylation (and other protein modification) and sorting and packagin proteins.
Gonadotropin releasing hormone (GnRH
A hormone released from the hypothalamus that triggers the anterior pituitary to secrete FSH and LH.
Gonadotropins
Anterior pituitary topic hormones FSH (follicle stimulating hormone) and LH (luteinizing homeon) that stimulates the gonads (testes and ovaries) to produce gametes and to secrete sex steroids.
G-protein linked receptor
A cell surface receptor associated with an intracellular protein that binds and hydrolyzes GTP. When GTP is bound, the protein is active, and can regulate the activity of adenylyl cyclease; this modifies the intracellular levels of second messenger cAMP. When the GTP is hydrolyzed to GDP, the protein becomes inactive again.
Graafian follicle
A large, mature, ovarian follicel with a well-developed antrum and a secondary oocyte. Ovulation of the oocyte occurs from this type of follicle.
Gram-negative bacteria
Bacteria that have a thin peptidoglycan cell wall covered by an outer plasma membrane. They stain very lightly (pink) in Gram stain. Gram-negative bacteria are typically more resistant to antibiotics than Gram-positive bacteria.
Gram-positive bacteria
Bacteria that have a thick peptido glycan cell wall, and no outer membrane. They stain very darkly (purple) in Gram stain.
Granulosa cells
the majority of the cells surrouding an oocyte in a follicle. Granulosa cells secrete estrogen during the follicular phase of the ovarian cycle (before ovulation).
Gray matter
Unmyelinated neuron cell bodies and short unmyelinated axons.
Growth hormone
A hormone released by the anterior pituitary that targets all cells in the body. Growth hormone stimulates whole body growth in children and adolescents, adn increases cell turnover rate in adults.
Guanine
One of the four aromatic bases found in DNA and RNA. Guanine is a purine; it pairs with cytosine.
Gustatory receptors
Chemoreceptors on the tongue that respond to chemicals in a food.
Gyrase
A prokaryotic enzyme used to twist teh single circular chromosome of prokaryotes upon itself to form supercois. Supercoiling helps to compact prokaryotic DNa and make it sturdier.
Hair cells
Sensory receptors found in the inner ear. Cochlear hair cells respond to vibration in the cochlea caused by sound waves and vestibular hair cells respond to changes in position and acceleration (used for balance).
Haploid organism
An organism that has only a single copy of its genome in each of its cells. Haploid organisms possess no homolous chromosomes.
Hardy-Weinberg law
A law of population genetics that states that the frequencies of alleles in a given gene pool do not change over time. There are five assumptions required for this law to hold true: there must be no mutation, there must be no migration, there must be no random mating between individuals in the population, and the population must be large. A population meeting all of these conditions, in which the allele frequency is not changing, is said to be in Hardy-Weinberg equilibrium.
hCG
Human Chorionic Gonadotropin, a hormone secreted by the trophoblast cells of a blasocyst (i.e. developing embryo) that prolongs the life of the corpus luteum, and thus increases the duration and amount of secreted progesterone. This helps to maintain the uterine lining so that menstruation does not occur. The presence of hCG in the blood or urine of a woman is used as a positive indicator of pregnancy.
Helicase
An enzyme that unwinds the double helix of DNA and separates the DNA strands in preparation for DNA replication.
Hematocrit
The percentage of wholeblood made up of erythrocytes The typical hematocrit value is between 40-45%.
Hematopoiesis
The synthesis of blood cells (occurs in the red bone marrow)
Hemizygous gene
A gene appearing in a single copy in diploid organisms, e.g. X-linked genes in human males.
Hemoglobin
A four-subunit protein found in red blood cells that binds oxygen. Each subunit contains a heme group, a large multi-ring molecule with an iron atom at its center. One hemoglobin molecule can bind four oxygen molecules in a cooperative manner.
Hemophilia
An X-linked recessive disorder in which blood fails to clot properly, leading to excessive bleeding if injured.
Hemostasis
The stoppage of bleeding; blood clotting.
Hepatic portal vein
A vein connecting the capillary bed of the intestines with the capillary bed of the liver. This allows amino acids and gluocse absorbed from the intestines to be delivered first to the liver for processing before being transported throughout the circulatory system.
Heterochromatin
DNA that is densely packed around histones. The genes in heterochromatin are generally inaccessible to enzymes and are turned off.
Heterotroph
An organism that cannot make its own food, and thus must ingest other organisms.
Heterozygous
A genotype in which two different alleles are possessed for a given gene.
Hexokinase
The enzymes that catalyzes the phosphorylation of glucose to form glucose-6-phosphate in the first step of glycolysis. This is one of the ain regulatory steps of this pathway. Hexokinase is feedback-inhibited by glucose-6-P.
Hfr bacterium
High frequency of recombination bacterium An F+ bacterium that has the fertility factor integrated into its chromosome. When conjugation takes place, it is able to transfer not only the F factor, but also its genomic DNA.
Histones
Globular protein that assist in DNA packaging in eukaryotes. Histones form octamers around which DNA is wound to form a nucleosome.
hnRNA
Heterogeneous nuclear RNA; the primary transcript made in eukaryotes before splicing.
Homeostasis
The maintenance of relatively constant internal conditions (such as temperature, pressure, ion balance, pH, etc.) regardless of external conditions.
Homologous chromosomes
A pair of similar chromosomes that have the same genes in the same order, but may have different versions (alleles) of those genes. One of the pair of chromosomes came from Mom in an ovum, and the other came from Dad in a sperm. Humans have 23 pairs of homologous chromosomes.
Homologous structures
Physical structures in two different organisms that have structural similarity due to a common ancestor, but may have different functions. Homologous structures arise from divergent evolution.
Homozygous
A genotype in which two identical alleles are possessed for a given gene. The allelles can both be dominant (homozygous dominant) or both be recessive (homozygous recessive)
Humoral immunity
Specif ic defense of the body by antibodies, secreted into the blood by B-cells.
Hydroxyapatite
Hardy crystals consisting of calcium and phosphate that form the bone matrix.
Hyperpolarization
The movement of the membrane potential of a cell away from rest potential in a more negative direction.
Hypodermis
Aso called a subcutaneous layer, this is a layer of *fat located under the dermis of the skin. The hypodermis helps to insulate the body and protects underlying muscles and other structures.
Hypophysis
The pituitary gland.
Hypothalamic-pituitary portal system
A set of veins that connect a capillary bed in the hypothalamus (the primary capillary plexus) with a capillary bed in the anterior pituitary gland (the secondary capillary bed). Releasing and inhibiting factors from the hypothalamus travel along the veins to directly affect cells in the anterior pituitary.
Hypothalamus
The portion of the diencephalon involved in maintaining body homeostasis. the hypothalamus also controls the release of hormones from the pituitary gland.
H zone
The region at the center of an A band of a sarcomere that is made up of myosin only. The H zone gets shorter (and may disappear) during muscle contraction.
I band
The regino of the sarcomere made up only of thin filaments. The I band is bisected by a Z line. I bands alternate with A bands to give skeletal and cardiac muscle a striated appearance. I bands get shorter (and may disappear completely) during muscle contraction.
Ileocecal valve
The sphincter that separates the final part of the small intestine (the ileum) from the fron part of the large intestine (the cecum). It is typically kept contracted (closed) so that chyme can remain in the small intestine as long as possible. The ileocecal valve is stimulated to relax by the presence of food in the stomach.
Ileum
The final section (approximately 55%) of the small intestine.
Implantation
The burrowing of a blastocyst (a developing embryo) into the endometrium of the uterus, typically occuring about a week after fertilizaiton.
Incomplete dominance
A situation in which a heterozygot displays a blended version of the pheotypes associated with each allele, e.g. pure-breeding white-flowered plants crossed with pure-breeding red-flowered plants produces heterozygous offspring plants with pink flowers.
Inducible enzymes
An enzyme whose transcription can be stimulated by an abundance of its substrate (as opposed to repressible enzyme). Usually in catabolism.
Induction
The process by which neighboring cells can influence the determination (and subsequent differentiation) of a cell.
Inflammation
An irritation of a tissue caused by infection or injury. Inflammation is characterized by four cardinal symptoms; redness (rubor), swelling (tumor), heat (calor), and pain (dolor).
Inhibin
A protein hormone secreted by sustenacular cells of the testes that acts to inhibit the release of FSH and LH from the anterior pituitary.
Innate immunity
General, non-specific protection to the body, including the skin (barrier), gastric acid, phagocytes, lysozyme, and complement.
Inner cell mass
The mass of cells in the blastocyst that ultimately give rise to the embryo and other embryonic structues (the amion, the umbilical vessels, etc.)
Inspiration
The movement of air into the respiratory tract. Inspiration is an active process, requiring contraction of the diaphragm.
Insulin
A peptide hormone produced and secreted by the Beta cells of the pancreas. Insulin targets cells in the body, especially the liver and muscle, and allows them to take glucose out of gthe blood (thus lowering blood glucose levels).
Integral membrane protein
A protein embedded in the lipid bilayer of a cell. These are typicallly cell surface receptors, channels, or pumps.
Intercalcated discs
The division between neighboring cardiac muscle cells. Intercalcated discs include gap junctions, which allow the cells to function as a unit.
Intercostal muscles
Muscles located in between the ribs that play a role in ventilation.
Interleukin
A chemical secreted by a T cell (usually the helper Ts) that stimulates activation and proliferation of other immune system cells.
Intermediate filaments
Cytoskeletal filaments with a diameter in between that of the microtubule and the microfilament. Intermediate filaments are composed of many different proteins and tend to play structural roles in cells.
Interneuron
A neuron found completely within the central nervous system. Interneous typically connect sensory and motor neurons, especially in reflex arcs.
Internodal tract
The portion of the cardiac conduction system between the SA node and the AV node.
Interphase
All of the cell cycle except for mitosis. Interphase includes G1, S phase, and G2.
Interstitial cell
Also called Leydig cells, these are teh cells within testes that produce and secrete testosteron. They are stimulated by luteinizing hormone (LH).
Intron
A nucleotide sequence that intervenes between protein-coding sequences. In DNA, these intervening sequences typically contain **regulatory sequences, however, in RNA they are simply spliced out to form the mature (translated) transcript.
Ion channel
A protein channel in a cell membrane that is specific for a particular ion, such as Na+ or K+. Ion channels may be constitutively open (leak channels), or regulated (voltage-gated or ligand-gated).
IPSP
Inhibitory postsynaptic potential; a slight hyperpolarization of the postysynaptic cell, moving the membrane potential of that cell further from threshold.
Iris
A pigmented membrane found just in from the lens of the eye. In the center of iris is the pupil, a hole through which light enters the eyeball. The iris regulates the diameter of the pupil in response to the brightness of light.
Islets of Langerhans
Also called simply, "islet cells" these are the endocrine cells of the pancreas. Different cell types wihtin the inslets secrete insulin, glucagon, and somatostatin
Jejunum
The middle (approximtely 40%) of the small intestine.
Juxtaglomerular apparatus (JGA)
A contact point between the afferent arteriole of the glomerulus and the distal convoluted tubule of the nephron. It is involved in regulating blood pressure.
Juxtaglomerular cells.
The cells of the afferent artery at the juxtaglomerular apparatus. They are baroreceptors that secrete renin upon sensing a decrease in blood pressure.
Keratin
A protein-based substance secreted by cells of the epiderms as they migrate outward. The keratin makes the cells tougher (better able to withstand abrasion) and helps make the skin waterproof.
Kinase
An enzyme that phosphorylates something else. Kinases are frequently used in regulatory pathways, phosphorylating other enzymes.
Krebs cycle
The third stage of cellular respiration, in which acetyl-CoA is combined with oxaloacetate to form citric acid. The citric acid is then decarboxylated twice and isomerized to recreate oxaloacetate. In the process, 3 molecules of NADH, 1 molecule of FADH2, and 1 molecule of GTP are formed (per acetyl-CoA)
Labia
The folds of skin that enclose the vaginal and urethral openings of females.
Labor contractions
Strong contractions of the uterus (stimulated by oxytoncin) that force a baby out of the mother's baby during childbirth. Labor contractions are part of a positive feedback cycle, during which the baby's head stretches the cervix, which stimulates stretch receptors that activate the hypothalamus, which stimulates the posterior pituitary to release oxytocin, which stimulates strong uterine contractions (labor contractions) that cause the baby's head to stretch the cervix. The cycle is broken once the baby is delivered.
Lacteals
Specialized lymphatic capillaries in the intestines that take up lipids as well as lymph.
Lactic acid
Produced in muscle cells from the reduction of pyruvate (under anaerobic conditions) to regenerate NAD+ so that glycolysis can continue. A rise in lactic acid usually accompanies an increase in physical activity.
Lacunae
Small cavities in the bone or cartilage that hold individual bones or cartilage cells.
Lagging strand
The newly forming daughter strand of DNA that is replicated in a discontinuous fashion, via Okazaki fragments that will ultimately be ligated together; the daugther strand that is replicated in the opposite direction that parallel DNA is unwinding
Lag phase
A short period of time **prior to exponential growth of a bacterial population during which no, or very limited, cell division occurs.
Large intestine
The final phase of the digestive tract, also called the colon. The primary funcion of the large intestine is to reabsorb water and to store the feces.
Larynx
A rigid structure at the top of the trachea (so it is part of trachea, I assume) made completely out of cartilage. The larynx has three main functions: (1) its rigidness ensures that the trachea is held open (provides an open airway). (2) the epiglottis folds down to seal the trachea during swallowing, thus directing food the espohagus, and (3) this is where the vocal cords are found (voice production).
Law of Independent Assortment
Mendel's seond law. States that genes found on different chromosomes, or genes found very far apart on the same chromosome (i.e., unlinked genes) sort independently of one another during gamete formation (meiosis).
Law of Segregation
Mendels' first law. The Law of Segregation states that the two alleles of a given gene will be separate from one another during gamete formation (meiosis).
Lawn
A dense grwoth of bacteria that covers the surface of a petri dish.
Leading strand
The newly forming daughter strand of DNA that is replicated in a continuous fasion; the daughter strand that is replicated in thes aem direction that parental DNA is unwinding.
Leak channel
An ion channel that is constitutively open, allowing the movement of teh ion across the plasma membrane according to its concentration gradient.
Length-tension relationship
The relationship of muscle length to its ability to generate strong contractions. Maximum tension (contraction strength) is achieved at sarcomere lengths between 2.0 and 2.2 microns. Tension decreases outside of this range <-- remember.
Leukocyte
A type of white blood cell; leukocytes are either B or T cells and are involved in disease defense.
Ligament
A strong band of connective tissue that connets bones to one another.
Ligand
The specific molecule that binds to a receptor.
Ligand-gated ion channel
An ion channel that is opened or closed based on the binding of a specific ligand to teh channel. Once opened, the channel allows the ion to cross the plasma membrane according to its concentration gradient. An examples is the acetylcholine receptor at the neuromuscular junction, which, when Ach binds, opens a cation channel in the muscle cell membrane.
Ligase
An enzyme that connects two fragments of DNA to make a single fragment; also called DNA ligase. This enzyme is usedd during DNA replication and is also used in recombinant DNA research.
Lipoprotein
Large conglomerations of proteins, fats, and cholesterol that transport lipids in the bloodstream. (chylomicrons are a type of lipoprotein).
Linkage
The failure of two separate genes to boey the Law of Independent Assortment, as might occur if the genes were found close together on the same chromosome.
Lipid
A hydrophobic molecule, usually fomred from long hydrocarbon chains. The most common forms in which lipids are found in the body are as triglycerides (energy storage), phospholipids (cell membranes), and cholestero (cell membranes and steroid synthesis).
Liver
The largest organ in the abdominal cavity. The liver has many roles, including procesing of carbohydrates and fats, synthesis of urea, production of blood proteins, production of bile, recycling heme, and storage of vitamins.
Local autoregulation
The ability of tissues to regulate their own blood flow in the absence of neural stiulation. THis is generally accomplished via metabolic wastes (such as CO2) that act as vasodilators.
Log phase
The period of exponential growth of bacterial population.
Long bone
The most common class of bone in the body, long bones have a well-defined shaft (the diaphysis) and two well-defined ends (the epiphyses).
Longitudinal muscle
The outer layer of smooth muscle in the wall of the digestive tract. When the longitudinal muscle contracts the tube shortens.
Loop of Henle
The loop of the nephron that dips downward into the renal medulla. The loop of Henle sets up a concentration gradient in the kidney such that from the cortex to the renal pelvis osmolarity increases. The descending limb of the loop of Henle is permeable to water, but not to sodium whereas the ascending limb is permeable to sodium, but not to water (and in fact, actively transports sodium out of the filtrate).
Loose connective tissue
Connective tissue that lacks great amount of collagen or elastic fibers (hence, loose), e.g., adipose tissue and areolar (general connective) tissue.
Lower esophageal sphincter
Formerly called the cardiac sphincter, this sphincter marks the entrance to the stomach. Its function is to prevent reflux of acid stomach contents into the esophagus; note that it does **not regulate entry into the stomach.
Lumen
The inside of the a hollow organ (e.g., the somach, intestines, bladder, etc.) or a tube (e.g., blood vessels, ureters, etc.)
Luteal phase
The third phase of the ovarian cycle, during which a corpus luteum is formed from the remnants of the follicle that has ovulated its oocyte. The corpus luteum secretes progestrone and estrogen during this time period, which typically lasts from day 15 to day 28 of the menstrual cycle. Formation of the corpul luteum is triggered by the same LH surge that triggers ovulation, however in the absence of LH (levels quickly decline after the surge) the corpus luteum begins to degenerate.
Luteinizing Hormone (LH)
A tropic hormone produced by the anterior pituitary gland that targets the gonads. In females LH triggers ovulation and the development of a corpus luteum during the menstrual cycle; in males, LH stimulates the production and release of testosteron.
Lymphatic system
A set of vessels in the body that runs alongside the vessels of the circulatory system. It is a one-way system, with lymphatic capillaries beginning at the tissues and ultimately emptying into the large veins near the heart. It serves to return excess tissue fluid (lymph) to the circulatory system, and filters the fluid through millions of white blood cells on its way back to the heart.
Lymph node
A concentrated region of white blood cells found along the vessels of the lympatic system.
Lymphocyte
The second most common of the five classes of leukocytes. Lymphocytes are involved in specific immunity and include two cell types, B-cells and T cells. B-cells produce and secrete antibodies and T-cells are invovled in cellular immunity.
Lymphokine
A chemical secreted by a T cell (usually the helper Ts) that stimulates activation and proliferation of other immune system cells.
Lysogenic cycle
A viral life cycle in which the viral genome is incorporated into the host genome where it can remain dormant for an unspecified period of time. Upon activation, the viral genome is excised from the host genome and typically enters the lytic cycle.
Lysosome
A eukaryotic organelle filled with digestive enzymes (acid hydrolases) that is involved in digestion of macromolecules such as worng organelles or material ingested by phagocytosis.
Lysozyme
An enzyme that lyses bacterial cell walls. Lysozyme is produced in the end stages of the lytic cycle so that new viral particles can escape their hosst; it is also found in human tears and human saliva.
Lytic cycle
A viral life cycle in which the host is turned into a "virus factory" and ultimately lysed to release the new viral particles.
Macrophage
A large, non-sepcific, phagocytic cell of the immune syste. Macrophages frequently leave the bloodstream to crawl around in the tissues and perform 'clean up' duties, such as ingesting dead cells or cellular debris at an injury site, or pathogens.
Macula densa
The cells of the distal tubule at the juxtaglomerular apparatus. They are receptors that monitor filtrate osmolarity as a means of regulatin filtration rate. If a drop is osmolarity is sensed, the macula densa dilates the afferent arteriole (to increase the blood pressure in the glomerulus and thus increase filtration) and stimulates the juxtaglomerular cells to secrete renin (to raise systemic blood pressure).
Maternal inheritance
Genes that are inherited only from the mother, such as mitochondrial genes (all organelles come only from the ovum).
Matrix
The interior of a mitochondrion (the region bounded by the inner membrane)., The matrix is the site of action of pyruvate dehydroganse complex and the Krebs cycle.
Mechanoreceptors
A sensory receptor that responds to mechanical disturbances, such as shape changes (being squashed, bent, pulled, etc.). Mechanoreceptors include touch receptors in the skin, hair cells, in the ear, muscle spindles, and others.
Medium
The environment in which or upon which bacteria grow. It typically contains a sugar source and any other nutrients that bacteria may require. 'Minimal medium' contain nothing but glucose.
Medulla
The inner region of an organ, e.g., the renal medulla, the ovarian medulla, and the adrenal medulla, etc.
Medulla oblongata
The portion of the hindbrain that controls respiratory and blood pressure, and specialized digestive and respiratory functions such as vomiting, sneezing, and coughing.
Meiosis
A type of cell division (in diploid cells) that reduces the number of chromosomes by half. Meiosis usualy produces haploid gametes in organisms that undergo sexual reproduction. It consists of a single interphase (G1, S, and G2) followed by two sets of chromosomal divisions, meiosis I and meiosis II. Meiosis I and II can both be subdivided into four phases similar to those in mitosis.
Melanin
A pigment produced by melanocytes in teh bottom cell layer of the epidermis. Melanin production is increased on sun exposure and helps prevent cllular damage due to UV radiation.
Memory cell
A cell produced when a B cell is activated by antigen. Memory cells do not actively fight the current infection, but patrol the body in case of future infection with the same antigen. If the antigen should appear again the future, memory cells are like 'preactivated' B cells, and can initiate a much faster immune response (the secondary immune response).
Meninges
The protective, connective tissue wrapping of the central nervous system (the dura mater, arachnoid mater, and pia mater).
Menopause
The perio dof tim ein a woman's life when ovulation and menstruation cease. Menopause typically begins in the late 40s.
Menstruation
The first phase of the uterine (endometrial) cycle, during which the endometrium from the previous cycle is shed off. Estrogen and progesterone levels are low during this time period. Menstruation typically lasts from day 1 to day 5 of the cycle.
Mesoderm
One of the three primary (embryonic) germ layers formed during gastrulation. Mesoderm ultimately forms 'middle' structures such as bones, muscles, blood vessels, heart, kindeys, etc.
Metaphase
The secon phase of mitosis. During metaphase chromosomes align at the center of the ell (the metaphase plate).
Metaphase I
The second phase of meiosis I. During metaphase I the paired homologous chromsomes (tetrads) align at the center of the cell (the metaphase plate).
Metaphase II
The second phase of meiosis II. Metaphase II is identical to mitotic metaphase, except that the number of chromosomes was reduced by half during meiosis I.
MHC
Major Histocompatability complex, a set of proteins found on the plasma membranes of cells that help display antigen to T cells. MHC I is found on all cells and displays bits of proteins from within the cell; this allows T cells to monitor cell contents and if abnormal peptides are displayed on the surface, the cell is destroyed by killer T cells. MHC II is found only on macrophages and B cells. This class of MHC allows these cells (known as antigen presenting cells) to display bitts of "eaten" (phagocytosed or internalized) proteins on their surface, allowing the activation of helper Ts --> thus further activating immune response.
Microfilament
The cytoskeleton filaments with the smallest diameter. Microfilaments are composed of the contractile protein actin. They are dynamic filaments, constantly beig made and broken down as needed, and are responsible for events such as pseudopod formation and cytokenesis during mitosis.
Microtubule
The largest of the cytoplasmic filaments. Microtubules are composed of two types of protein, alpha tubulin and beta tubulin. They are dynamic fibers, constantly being built up and broken down, according to cellular needs. Microtubules form the mitotic spindle during cell division, form the base of cilia and flagella, and are used for intracellular structure and transport.
Microvilli
Microscopic outward folds of the cells lining the small intestine; microvilli serve to increase the surface area of the small intestine for absorption.
Midbrain
The portion of the brain responsible for visual and auditory startle reflexes.
Milk letdown
The release of milk from the mammary glands via contraction of ducts within the glands. Contraction is stimulated by oxytocin, which is released from the posterior pituitary when the baby begins nursing.
Missense mutation
A point mutation in which a codon that specifies an amino acid is mutated into a codon that specifies a different amino acid.
Mitochondrion
An organelle surrounded by a double=membrane (two lipid bilayers) where ATP production takes place. The interior (matrix) is where PDC and the Krebs cycle occur, and the inner membrane contains the enzymes of the electron trasport chain and ATP synthase.
Mitosis
The phase of the cell cycle during which the replicated genome is divided. Mitosis has four phases (prophase, metaphase, anaphase, telophase) and includes cytokinesis (the physical splitting of the cell into two new cells).
Monocistronic mRNA
mRNA that codes forsingle type of protein, such as is found in eukaryotic cells.
Monosaccharide
The monomer of a carbohydrate. Monosaccharides have the general chemical formula CnH2nOn, and common monosaccharides include glucose, fructose, galactose, and ribose.
Morula
A solid clump of cells resulting from cleavage in the early embryo. Because there is very little growth of these cells during cleavage, the morula is ony about as large as the original zygote.
Motor end plate
The portion of the cell membrane at the neuromusclar junction; essentially the postsynaptic membrane at the synapse.
Motor unit
A motor neuron and all the all the skeletal muscle cells it innervates. Large motor units are typically found in large muscles (e.g., the thighs and buttocks) and produce fross movements. Small motor untis are found in smaller muscles (e.g. the rectus muscles that controle movements of the eyeball, the fingers) and produce more precise movements.
Motor unit recruitment
A mechanism for increasing tension (contractile length) in a muscle by activating more motor units.
mRNA
Messenger RNA; the type of RNa that is read by a ribosome to synthesize protein.
Mucocilliary escalator
The layer of ciliated, mucus-covered cells in the respiratory tract.The cilia continually beat, sweeping contaminated mucus upward toward the pharynx.
Mucosa
The layer of epithelial tissue that lines body cavities in contact with the outside environment (respiratory, digestive, urinary, and reproductive tracts).
Mullerian ducts
Earlier embryonic ducts that can develop into femal internal genitalia in the absence of testosteron.
Mullerian inhibiting factor (MIF)
A substance secreted by embryonic testes that causes the regression of the Mullerian ducts.
Multipolar neuron
A neuron with a single axon and multiple dendrites; the most common type of neuron in the nervous system.
Mutualism
A form of symbiosis in which both organisms involved benefit from the association.
Myelin
An insulating layer of membranes wrapped around the axons of almost all neurons in the body. Myelin is essentially the plasma membranes of specialized cells; Schwann cells in the peripheral nervous system, and oligodendrocytes in the central nervous system.
Myofiber
A skeletal muscle cell, also known as a muscle fiber. Skeletal muscle cells are formed from the fusion of many smaller cells (during development) consequently they are very long and are multinucleate.
Myofibril
A string of sarcomeres with a skeletal muscle cell (hence smaller than myofiber). Each muscle cell contains hundreds of myofibirils.
Myoglobin
A globular protein found in muscle tissue that has the ability to bind oxygen. Myoglobin helps to store oxygen in the muscle for use in aerobic respiration (it does not move, just stays there). Muscles that participate in endurance activities (including cardiac muscle) have abundant supplies of myoglobin.
Myometrium
The muscuar layer of the uterus. The myometrium is made of smooth muscles that retains its ability to divide in order to accomodate the massive size increases that occur during pregnancy. The myometrium is stimulated to contract during labor by the hormone oxytocin.
Myosin
One of the contractie proteins in muscle tissue. In skeletal and cardiac muscles, myosin forms the thick filaments. Myosin has intrinsic ATPase activity and can exist in two conformation, either high energy or low energy.
Myosin light-chain kinase (MLCK)
A kinase in smooth muscle cells activated by calmodulin the presence of Ca2+. As its name implies, this kinase phosphorylates myosin, activating it so that muscle contraction can occur.
NADH
The reduced form of NAD+ (nicotinamide adenine dinucleotide). This is the most common electron carrier in cellular respiration.
Na+/K+ ATPase
A protein found in the plasma membrane of all cells in the body that uses the energy of an ATP (hydrolyzes ATP) to move three Na+ ions out of the cell and two K+ ions into the cell, thus establishing concentrations gradients for these ions across the cell membrane.
Natural selection
The mechanism described by Charles Darwin that drives evolution. Through mutation, some organisms possess genes that make them better adapted to their environment. These organisms survive and reproduce more than those that do not possess the beneficial genes, thus these genes are passed on to offspring, making the offspring better adapted. Over time, these genes (and the organisms that possess them) become more abundant, and the less beneficial genes (and the organisms that possess them) become less abundant.
Nephron
The function unit of the kidney. Each kidney has about a million nehprons; this is where blood filtration and subsequent modification of the filtrate occurs. The nephron empties into collecting ducts, which empty into the ureter.
Neuron
The basic functional and structural unit of the nervous system. The neuron is a highly specialized cell, designed to transmit action potentials.
Neuromuscular junction
The synapse between a motor neuron and a muscle cell. At the NMJ, the muscle cel lmembrane is invaginated and the axon terminus is elongated so that a greater area of membrane can be depolarized at one time.
Neurotransmitter
A chemical released by the axon of a neuron in response to an action potential that binds to receptors on a postsynaptic cell and causes that cell to either depolarize slightlly (EPSP) or hyperpolarize slightly (IPSP). Examples are acetylcholine, norepinephrine, GABA, dopamine, and others.
Neuralation
The formatino of the nervous system during weeks 5-8 of gestation. Neuralation begins when a section of the ectoderm invaginates and pinches off to form the neural groove, which ultimately forms the neural tube, from which the brain and spinal cord develop.
Nociceptors
Pain receptors. Nociceptors are found everywhere in the body except for the brain.
Nodes of Ranvier
Gaps in the myelin sheath of the axons of peripheral neruons. Action potentials can 'hump' from node to node, thus increasing the speed of conduction (saltatory conduction).
Noncompetitive inhibitor
An enzyme inhibitor that binds at a site other than the active sit of an enzyme (binds at an allosteric site). THis changes the three-dimensional shape of the enzyme such that it can no longer catalyze the reaction
Nondisjunction
The failure of homologous chromosomes or sister chromatids to separate properly during cell division. This could ocur during anaphase I of meiosis (homologous chromosomes) [--> leaving 2 gametes w/ 2 copies and 2 gametes w/ no copies of chromosome], or during anaphase II of meiosis or *anaphase of mitosis (sister chromatids).
Nonsense mutation
A point mutation in which a condon that specifies an amino acid is mutated into a stop (nonsense) codon.
Norepinephrine
The neurotransmitter used by the sympathetic division of the ANS at the postganglionic (organ-level ) synapse.
Nuclear envelope
The membrane surrounding the DNA in eukaryotic cells made of two lipid bilayers.
Nuclear localization sequence
A sequence of amino acids (usually basic) that directs a protein to the nuclear envelope, where it is imported by a specific transport mechanism.
Nuclear pore
A protein channel in the nuclear envelope that llows the free passage of molecules smaller than 60 kD.
Nucleolus
A region within the nucleus where rRNA is transribed and ribosomes are partially assembled.
Nucleoside
A structure composed of a ribose molecule linked to one of the aromatic bases. In a deoxynucleoside, the ribose is replaced with deoxyribose.
Nucleosome
A structure composed of two coils of DNA wrapped around an octet of histone proteins. The nucleosome is the primary form of packagin of eukaryotic DNA.
Nucleotide
A nucleoside with one or more phosphate gropus attached. Nucleoside triphosphates (NTPs) are the building blocks of RNA and are also used as energy molecules, especially ATP. Deoxynucleoside triphosphates (dNTPs) are the building blocks of DNA; in these molecules, the ribose is replaced with deoxyribose.
Nucleus
An organelle bounded by a double membrane (double lipid bilayer) called the nuclear envelope. The nucleus contains the genome and is the site of replication and transcription.
Linker DNA
The string between beads of DNA on histones. They are also wrapped around a single histone, called linker histone - may not really have to know..
Obligate aerobe
An organism that requires oxygen to survive (aerobic metabolism only).
Obligate anaerobe
An organism that can only survive in the absence of oxygen (anaerobic metabolism); oxygen is toxic to obligate anaerobes.
Okazaki fragments
Small fragments of DNa produced on the lagging strand during DNa replication, joined later by DNA ligase to form a complete strand.
Olfactory receptors
Chemoreceptors in the upper nasal cavity that respond to odo chemicals.
Oncotic pressure
The osmotic pressure in the blood vessels due only to plasma proteins (primarily albumin) --> causes water to rush back into capillaries at end.
Oogonium
A precursor cell that undergoes mitosis during fetal development to produce more oogonium. These cells are then activated to produce primary oocytes, which remain dormant until stimulated to undergo meiosis I during some future menstrual cycle.
Operator
A specific DNA nucleotide sequence where transcriptional regulatory proteins can bind.
Operon
A nucleotide sequence on DNA that contians three elemtns: a coding sequence for one or more enzymes, *a coding sequence for a regulatory protein, and upstream regulatory sequences where the regulatory proteins can bind. An example is the lac operon found in prokaryotes.
Optic disk
The 'blind spot' of the eye, this is where the axons of the ganglion cells exist the retinal to form the optic nerve. There are no photoreceptors in the optic disk.
Optic nerve
The nerve extending from the back of teh eyeball to teh brain that carries visual information. The ptic nerve is made up of the axons of the ganglion cells of the retina.
Organ of Corti
The structure in the cochlea of the inner ear made up of the basilar membrane, the auditory hair cells, and the tectorial membrane. The Organ of Corti is the site where auditory sensation is detected and transduced to action potentials.
Organogenesis
The stage of human development during which the organs are formed. Organogenesis begins after gastrulation and is completed by the eight week of gestation.
Orgasm
A function of the reproductive system controlled by the sympathetic nervous system. In males, organs includes emission and ejaculation; in females it is mainly a series of rhythmic contraction of the pelvic floor muscles and the uterus.
Origin of replication
The specific location on a DNa strand where replication begins.. Prokaryotes typically have a single origin of replication, while eukaryotes have several per chromosome.
Osmosis
The movement of water (the solvent) from its region of high concentration to its region of low concentration. NOte that the water concnetration gradient is opposite to the solute concentration gradient, since where solutes are concentrated, water is scarce.
Osmotic pressure
The force required to resist the movement of water by osmosis. Osmotic pressure is essentialy a measure of the concentration of a solution. A solution that is hyighly concnetrated has a strong tendency to draw water into itself, so the pressure required to resist that movement would be high. Thus, highly concentrated solutions are said to have high osmotic pressures.
Ossicles
The three small bones found in the middle ear (the malleus, the incus, and the stapes) that help to amplify the vibrations from sound waves. The malleus is atached to the tympanic membrane and the stapes is attached to the oval window of the cochlea.
Osteoblast
A cell that produces bone.
Osteoclast
A phagocytic-like bone cell that breaks down bone matrix to release calcium and phosphate into the bloodstream.
Osteocyte
A mature, dormant osteoblast.
Osteon
The unit of combact bone, also called a Haversian system. Osteons are essentially long cylinders of bone; the hollow center is called the central canal, and is where blood vessels, nervs, and lymphatic vessels are found. Compact bone is laid down around the central canal in rings (lamellae).
Outer ear
The portion of the ear consisting of the pinna and the external auditory canal. The outer ear is separated from the middle ear by the tympanic membrane (the eardrum).
Oval window
The membrane that separates the middle ear from the inner ear.
Ovarian cycle
The 28 days of the menstrual cycle as they apply to events in the ovary. The ovarian cycle has three subphases: the follicular phase, ovulation, and the luteal phase.
Ovary
The female primary sex organ. The ovary produces female gametes (ova) and secretes estrogen and progesterone.
Ovulation
The release of a secondary oocyte (along with some granulosa cells) from the ovary at the approximate midpoint of the menstrual cycle (typically around day 14). Ovulation is triggered by a surge in LH.
Oxaloacetate
A four-carbon molecule that binds with the two-carbon acetyl unit of acetyl-CoA to form citric acid in the first step of the Krebs cycle.
Oxidation
To attach oxygen, to remove hydrogen, or to remove electrons from a molecule.
Oxidative phosphorylation
The oxidation of high-energy electron carriers (NADH and FADH2) coupled to the phosphorylation of ADP, producing ATP. In eukaryotes, oxidative phosphorylation occurs in the mitochondira.
Oxytocin
A hormone released by the posterior pituitary that stimulates uterine contractions during childbirth and milk ejection during breastfeeding.
Pacemaker potential
A self-initiating action potential that occurs in the conduction system of the heart and triggers action potentials (and thus contraction) in the cardiac muscle cells Tee pacemaker potential is triggered by the regular, spontaneous depolarization of the cells of the conductions system, due to slow inwar leak of positive ions (Na+ and Ca2+). Because the SA node has the fastest leak, it typically reaches the threshold for the pacemaker potential before any other region of the conduction system, and thus sets the pace of the heart.
Pancreas
An organs in the abdominal cavity with two roles. The first is an exocrine role: to produce digestive enzymes and bicarbonate, which are delivered to the small intestine via the pancreatic duct. The second is an endocrine role: to secrete insulin and glucagon into the bloodstream to help regulate blood glucose levels.
Pancreatic duct
The main duct of the pancreas. The pancreatic duct carries the exocrine secretions of the pancreas (enzymes and bicarbonate) to the small intestine (dueodenum).
Parasite
An organism that requires the aid of a host organism to survive, and that harms the host in the process.
Parasympathetic nervous system
The division of the autonomic nervous system known as the 'resting and digesting' system. It causes a general decrease in body activities such as heart rate, respiratory rate, and blood pressure, and an increase in blood flow to the GI tract and digestive function. Because the preganglionic neurons all originate from either the brain or the sacrum, it is also known as the craniosacral system.
Parathyroid hormone (PTH)
A hormone produced and secreted by the parathyroid glands that increases serum calcium levels. It targets the bones (stimulates osteoclasts), the kidneys (increases calcium reabsorption), and the small intestine (increases calcium absorption).
Parietal cells
Cells found in gastric glands that secrete hydrochloric acid (for hydrolysis of ingested food) and gastric intrinsic factor (for absorption of vitamin B-12).
Partial pressure
The contribution of an individual gas to the total ppressure of a mixture of gases. Partial pressures are used to describe the amounts of the various gases carried in the bloodstream.
Passive transport
Movement across the membrane of a cell that does not require energy input from the cell. Passive transport relies on concentration gradients to provie the driving force for movement, and includes both simple and facilitated diffusion.
Penetrance
The percentage of individuals with a particular genotype that actually displays the phenotype associated with the genotype.
Penetration
The second step in viral infection, the injection of the viral genome into the host cell.
Pepsin
A protein-digesting enzyme secreted by the chief cells of the gastric glands. Pepsin is secreted in its inactive form (pepsinogen) and is activated by gastric acid. It is unusual in that its pH optimum is around 1-2; most of these enzymes in the body function best at neutral pHs
Peptide bond
The bond formed between the carboxyl group of one amino acid and the amino group of another.
Peptide hormone
A hormone made of amino acids (in some cases just a single, modified amino acid). Peptide hormones are generally hydrophilic and cannot cross the plasma membranes of cells, thus receptor for peptide hormones must be found on the cell surface. An exception is thyroxine, which is hydrophobic enough to enter the cells easily. Binding of a peptide hormone to its receptor usually triggers a second messenger system within the cell.
Peptidoglycan
A complex polymer of sugars and amino acids; the substance from which bacterial ell walls are made.
Perfusion
The flow of blood through a tissue; ischeia is when there is no blood flow, anoxia when there is no O2 available (ischemia is more dangerous b/c of waste build-up)
Peripheral chemoreceptors
Receptors in the carotid arteries and the aorta that monitor blood pH to help regulate ventilation rate.
Peripheral membrane protein
A protein that is associated with the plasma membrane of a cell, but that is not embedded in the lipid bilayer. Peripheral proteins typically associate with embedded proteins through hydrogen bonding or electrostatic interactions.
Periperal nervous system
All parts of the nervous system except for the brain and spinal cord.
Peripheral resistance
The resistance to blood flow in the systemic circulation. Peripheral resistance increases if arteries constrict (diameter decreases), and an increase in peripheral resistance leads t o an increase in blood pressure.
Periplasmic space
The space between the inner and outer cell membranes in Gram-negative bactera. The peptidoglycan cell wall is found in the periplasmic space, and this space sometimes contains enzymes to degrade antibiotics.
Peristalsis
A wave of contraction that sweeps along a muscular tube, pushing substances along the tube (e.g., food through the digestive tract, urine through the ureters, etc.)
Peroxisome
Small organelles that contain the hydrogen peroxide produced as a byproduct of lipid metabolism. Peroxisomes convert hydrogen peroxide to water and oxygen by way of the enzyme catalase.
Phagocytosis
The non-specific uptake of solid material by a cell accomplished by englufing the particle with plasma membrane and drawing it into the cell.
Pharynx
A passageway leading from behind the nasal cavity to the trachea. The pharynx is divided into three regions, named for their location. The nasopharynx is behind the nasal cavity, the oropharynx is behind the oral cavity, and the laryngopharynx is behind the larynx. The nasopharynx is a passageway for air only, but the oropharynx and laryngopharynx are passageways for both air and food; consequently they are lined with a much thicker layer of cells to resis damage due to abrasion.
Phenotype
The physical characterisitcs resulting from the genotype. Phenotypes are usually described as dominant or recessive.
Phosphofructokinase
The enzyme that catalyzes the phosphorylation of fructose-6-phosphate to form fructose-1-6-bisphosphate in the third step of glycolysis. This is the main regulatory step of glycolysis. PFK is feedback-inhibited by ATP.
Phospholipid
The primary membrane lipid. Phospholipids consist of a glycerol molecule esterified to two fatty acid chains and a phosphate molecule. Additional, highly hyrohpilic groups are attached to the phosphate, making this molecule extremely amphipathic.
Photoreceptor
A receptor that responds to light
Phototroph
An organism that utilizes light as its primary energy source.
Pilus
A long projection on a bacterial surface involved in an attachment, e.g., the sex pilus attaches F+ and F- bacteria during conjugation.
Pinocytosis
The non-specific uptake of liquid particles into a cell by invagination of the plasma membrane and subsequent 'pinching off' a small bit of the extracellular fluid.
Placenta
An organ that develops during pregnacy, derived in part from the mother and in part from the zygote. The placenta is the site of exchange of nutrients and gases between the mother's blood and the fetus' blood. The placenta is formed during the first three months of pregnancy.
Placental villi
Zygot-derived projections that extend into the endometrium of the uterus during pregnancy. Fetal capillaries grow into the placental villi, which are surrounded by a pool of maternal blood. THis facilitates nutrient and gas exchange between the mother and the fetus, without actually allowing the blood to mix.
Plaque
A clear area in a lawn of bacteria. Plaques represent an area where bacteria are lysing (dying) and usually caused by a lytic virus.
Plasma
The liquid portion of blood; plasma contains water, ions, buffers, sugars, proteins, etc. Anything that dissolves in blood dissolves in the plasma portion.
Plasma cell
An activated B cell that is secreting antibody.
Plasmid
A small, extrachromosomal (outside the genome), circular DNA molecule found in prokaryotes.
Platelets
Extremely small pseudo-cells in the blood, important for clotting. They are not true cells, but are broken-off bits of a larger cell (a megakaryocyte).
Pleiotropic gene
A gene that has effects on several different characteristics.
Pleura
The membranes that line the surface of the lungs (visceral pleura) and the inside wall of the chest cavity (parietal pleura).
Pleural pressure
The pressure in the (theoretical) space between the lung surface and the inner wall of the chest cavity.
Point mutation
A type of mutation in DNa where a single base is substituted for another.
Polar body
A small cell with extremely little cytoplasm that results from the unequal cytoplasmic divsion of the primary (produces the first polar body) and the secondary (produces the second polary body) oocytes during meiosis (oogenesis). The polar bodies degenerate.
Poly-A tail
A string of several hundred adenine nucletodies added to the 3' end of the eukaryotic mRNA.
Poycistronic mRNA
mRna that codes for several different proteins by utliizing different reading frames, nested genets, etc. Polycistronic mRNa is a characteristic of prokaryotes.
Polysaccharides
A molecule formed by joining many monosaccharides together. POlysaccharides are typically energy-storage molecules (glycogen in animals, starch in plants) or structural molecules (cellulose in plants, chitin in exoskeletons).
Polyspermy
The fertilization of an oocyte by more than one sperm. This occurs in some animals, but in humans, blocks to polyspermy exist (the fast block and the slow block) so that only a single sperm can penetrate the oocyte.
Population
A subset of a species consisting of members that mate and reproduce with one another.
Pore
A pathway through a plasma membrane that restrics passage based only on the size of the molecules. Pore are made from porin proteins.
Portal systems
A system of blood vessels where the blood passes from arteries to capillaries to veins, then through a second set of capillaries, and then through a final set of veins. THere are two portal systems in the body, the hepatic portal system and the hypothalamic portal system.
Posterior pituitary gland
Also known as the neurohyophysis, the posterior pituitary is made of nervous tisssue and stores and secretes two hormones made by the hypothlamus; oxtytocin and ADH. The posterior pituitary is controlled by action potentials from the hypothalamus.
Postganglionic neuron
In the autonomic division of the PNS, a neuron that has its cell body located in the autonomic ganglion (where a preganglionic neuron synapses with it) and whose axon synapses with the target axon.
Potassium leak channel
An ion channel specific for potassium found in the plasma membrane of all cells in the body. Leak channels are constitutively open and allow their specifi ion to move across the membrane according to its gadient. Potassium leak channels allow potassium to leave the cell.
Power stroke
The step in the sliding filament theory during which yosin undergoes a conformaitonal change to its low energy state, in the process dragging the thin filaments (and the attached Z lines) toward the center fo the sarcomere. NOte that power stroke requires ATP only indirectly: to se the myosin molecule in its high-energy conformation during a different step of the sliding filament thoery.
Preganglionic neuron
In the autonomic divison of the PNS, a neuron that has its cell body located in the CNS, and whose axon extends into the PNS to synapse with a second neuron at an autonoic ganglion. (The second neuron's axon synapses with the target axon)
Primary active transport
Active transport that relies directly on the hydrolysis of ATP.
Primary bronchi
The first branches of the trachea. There are two primary bronchi, one for each lung.
Primary immune response
The first encounter with an antigen, resuling in activated B cells (antibody secretion) and T cells (cellular lysis and lymphocyte proliferation). The primary immune response takes approximately ten days, which long enough for symptoms of the infection to appear (because initial activation takes long time).
Primary oocytes
Diploid cells resulting from the activation of anoogoium; primary oocytes are ready to enter meiosis I. remember: cyte means ready to undergo meiosi
Primary spermatocytes
Diploid cells resultinf rom the activation of a spermatogoium; primary spermatocytes are ready to enter meiosis I. remember: cyte means ready to undergo meiosis.
Primase
An RNA polymerase that creates a primer (made of RNA) initiate DNa replication. DNA pol binds to the primer and elongates it.
Productive cycle
A life cycle of animal viruses in which the mature viral particles bud from the host cell, acquiring an envelope (a coating of lipid bilayer) in the process.
Progesterone
A steroid hormone produced by the corpus luteum in the ovary during the second half of the menstrual cycle Progesterone maintains and enhances the uterine lining for the possible implantation of a fertilized ovum. It is the primary hormone secreted during pregnancy.
Prokaryote
An organism that lacks a nucleus or any other memrane-bound organelles. All prokaytes belong to the Kingdom Monera (not protista!)
Prolactin
A hormone secreted by the anterior pituitary that tarets the mammary glands stimulating them to produce breastmilk.
Proliferative phase
The second phase of the uterine (endometrial) cycle, during which the endometrium (shed off during menstration is rebuilt). This phase of the cycle is under the control of estrogen, secreted from the follicle developing in the ovary during this time period. The proliferative phase typically lasts from day 6 to day 14 of the menstrual cycle.
Promoter
The sequence of nucleotides on a chromosome that activates RNA polymerase so that transcription can take place. The promoter is found upstream of the start site, the location where transcription actually takes place.
Prophase
The first phase of mitosis. During prophase the replicated chromosomes condense, the spindle is formed, and the nuclear envelope breaks apart into vessicles.
Prophase I
The first phase of meiosis I. During prophase I the replicated chromosomes condense, homologous chromsomes pair up, crossing over occurs between homologous chromosomes, the spindle is formed, and the nuclear envelope breaks apart into vesicles. Prophase I is the longest phase of meiosis.
Prophase II
The first phase of meiosis II. Prophase II is identical to mitotic prophase, except that the number of chromosomes was reduced by half during meiosis I.
Proprioreceptor
A receptor that responds to changes in body position, such as stretch on a tendon, or contraction of a muscle. These receptor allow us to be consciously aware of the position of our body parts.
Prostate
A small gland encircling the male urethra just inferior to the bladder (only reproductive structure not paired). Its secretion contain nutrients and enzymes and account for approximately 35% of the ejaculate volume.
Prosthetic group
A non-protein, but organic, molecule (such as vitamin) that is covalently bound to an enzyme as part of the active site.
Proteins
Molecules made by connecting amino acids via peptide bonds. Proteins are synthesized (translated) by ribosomes, and function as enzymes, carriers, structrual fibers, cell surface receptors, channels, porters, hormones, etc.
Proximal convoluted tubuel
The first portion of the nephron tubuel after the glomerulus. THe PCT is the site of most reabsorption; all filtered nutrients are reabsorbed here as well as most of the filtered water.
P site
Peptidyl-tRNA site; the stie on a ribosome where the growing peptide (attached to a tRNA) is found during translation.
Ptyalin
Salivary amylase
Pulmonary artery
The blood vessel that carries deoxygenated from the right ventricle of the heart to the lungs.
Pulmonary circulation
The flow of blood from the heart, through the lungs, and back to the heart.
Pulmonary edema
The collection of fluid in the alveoli, particularly dangerous because it impedes gas exchange. Common causes of pulmonary edema are increased pulmonary blood pressure or infection of the respiratory system.
Pulmonary vein
One of several vessels that carry oxygenated blood from the lungs to the left atrium of the heart.
Pupil
A hole in the center of the iris of the eye that allows light to enter the eyeball. The diameter of pupil is controlled by the iris in response to the brightness of the light.
Purine bases
Aromatic bases found in DNA and RNA that are derived from purine. They have a double rightn structure and include adenine and guanine.
Purkinje fibers
The smallest (and final) fibers in the cardiac conduction system. The Purkinje fibers transmit the cardiac impulse to the ventricular muscle.
Pyloric sphincter
The valve that regulates the passage of chyme from the stomach into the small intestine.
Pyrimidine bases
Aromatic bases found in DNa and RNA that have a single-ring structure. They include cytosine, thymine, and uracil.
Pyruvate dehydrogenase complex
A group of three enzymes that decarboxylates pyruvate, creating an acetyl group and carbon dioxide. The acetyl group is then attached to coenzyme A to produce acetyl-CoA, a substrate in the Krebs cycle. In the process, NAD+ is reduced to NADH. The pyruvate dehydrogenase complex is the second stage of cellular respiration.
Pyruvic acid
The product of glycolysis; 2 pyruvic acid (pyruvate) molecules are produced from a single glucose molecule. In the absence of oxygen, pyruvic acid undergoes fermentation and is reduced to either lactic acid or ethanol; in the presence of oxygen, pyruvi acid is oxidized to produce acetyl-CoA, which can enter the Krebs cycle.
Receptor-mediated endocytosis
A highly specific cellular uptake mechanism. The molecule to be taken up must bind to cell surface receptor found in a clathrin-coated pit.
Recessive
The allele in a heterozygou genotype that is not expressed; the phenotype resulting from possession of two recessive alleles (homozygous recessive).
Recombination frequency
The RF value, the percentage of recombinant offspring resulting from a given genetic cross. The recombination frequency is proportional to the physical distance between genes on a chromosome. If a recombination frequency is low, the genes under consideration may be linked.
Rectum
The final portion of the large intestine.
Reduction
To remove oxygen, to add hydrogen, or to add electrons to a molecule.
Reflex arc
A relatively direct connection between a sensory neuron and a motor neuron that allows an extremely rapid response to a stimulus, often without conscious brain involvement.
Relative refractory period
The period of time following an action potential when it is possible, but difficult, for the neuron to fire a second action potential due to the fact that membrane is further from theshold potential (hyperpolarized).
Release factor
A cytoplasmic protein that binds to a stop codon where it appears in the A-site of the ribosome. Release factors modify the peptidyl transferase activity of the ribosome, such that a water molecule is added to the end of the completed protein. This releases the finished protein from the final tRNA, and allows the ribosome subunits and mRNA to disassociate.
Renal absorption
The movement of a substance from the filtrate (in the renal tuble) bak into the bloodstream. Reabsorption reduces the amount of a substance in the urine.
Renal tubule
The portion of the nephron after the glomerulus and apsule; the region of the nephron where the filtrate is modified along its path to becoming urine.
Renin
An enzyme secreted by the juxtaglomerular cells when blood pressure decreases. Renin onverts angiotensinogen to angiotensin I.
Replication
The duplication of DNA
Relication fork(s)
The site(s) where the parental DNA double helix unwinds during replication.
Replication bubbles
Multiple sites of replication found on large, linear eukaryotic linear eukaryotie chromosomes.
Repolarization
The return of membrane potential to normal resting values after a depolarization of hyperpolarization.
Repressible enzyme
An enzyme whose transcription can be stopped by an abundance of its product (as opposed to inducible enzymes). Usually part of anabolism of product.
Repressor
A regulatory protein that binds DNA at a specific nucleotide sequence (sometimes known as the operator) to prevent transcription of downstream genes.
Residual volume
The volume of air remaining in the lungs after a maximal forced exhalation, typically about 1200 mL.
Resolution
A function the reproductive system (conrolled by the sympathetic nervous system) that returns the body to its normal resting state after sexual arousal and orgasm.
Respiratory acidosis
A drop in blood pH due to hypoventilation (too little breathing) and a resulting accumulation of Co2.
Respiratory alkalosis
Arise in blood pH due to hyperventilation (excessive breathing) and a resulting decrease in CO2.
Resting membrane potential
An electrical potential established across the plasma membrane of all cells by the Na+/K+ ATPase and the K+ leak channels. IN most cells, the resting membrane potential is approximately -70 mV with respect to the outside of the cell.
Restriction endonuclease
A bacterial enzyme that recognizes a specific DNA nucleotide sequence and that cuts the double helix at a specific site within the sequence.
Retina
The innermost layer of the eyeball. The retina is made up of a layer of photoreceptors, a layer of bipolar cells, and a layer of ganglion cells.
Retinal
A chemical derived from vitamin A found in the pigment proteins of the rod photoreceptors of the retina. Retinal changes conformation when it absorbs light, triggering a series of reactions that ultimately result in an action potential being sent to the brain.
Retrovirus
A virus with an RNA genome (e.g. HIV) that undergoes a lysogenic life cycle in a host with a double stranded DNA genome. In order to integrate its genome with the host cell genome, the virus must first reverse trasncribe its RNA genome to DNA.
Reverse transcriptase
An enzyme that polymerizes a strand of DNA by reading an RNA template (an RNA dependent DNa polymerase); used by retrovirus in order to integrate their genome with the host cell genome.
Ribosome
A structure made of two protein subunits and rRNA; this is the site of protein synthessis (translation) in a cell. Prokaryotic ribosomes (also known as 70S ribosomes) are smaller than eukaryotic ribosome (80S ribosomes). The S value refers to the sedimentation rate during centrifugation.
RNA dependent RNA polymerase
A viral enzyme that makes a strand of RNA by reading a strand of RNa . All prokaryotic and eukaryotic RNa polymerases are DNa dependent; they make a strand of RNa by reading a strand of DNA.
RNA polymerase
An enzyme that transcribes RNa. Prokaryotes have a single RNA pol, while eukaryotes have three; in eukaryotes, RNA pol I transcribes rRNA, RNA pol II transcribes mRNA, and RNA pol III transcribes tRNA.
Rods
Photoreceptors in the retina of the eye that respond to dim light and provide us with black and white vision.
Rough endoplasmic reticulum
A large system of folded membranes within a eukaryotic cell that has ribosomes bound to it, giving a rough appearnce. These ribosomes synthesize proteins that will ultimately be secreted from the cell, incorporated into the plasma membrane, or transported to the Golgi apparatus or lysosome.
rRNA
Ribosomal RNA; the type of RNA that associates with ribosomal proteins to make a functional ribosome. It is thought that the rRNA has the peptidyl transferase activity.
Rule of addition
A statistical rule stating that the probability of either of two indpendent (and mutually exclusive) events ocuring is the sum of their individual probabilities minus the probability of them both occuring together.
Rule of multiplication
A statistical rule stating that the probability of two independent events occuring together is the product of their individual probabilities.
Saltatory conduction
A rapid from of action potential conduction along the axon of a neuron in which the action potential appears to jump from nodde of Ranvier to node of Ranvier.
Saprophyte
An organism (such as a fungus) that feeds of dead plants and animals.
Sarcolemma
The plasma membrane of a muscle cell.
Sarcomere
The unit of muscle contraction. Sarcomeres are bounded by Z lins, to which thin filaments attach. Thick filaments are found in the center of the sarcomere, overlapped by thin filaments over one another during contraction reduces the distance between Z lines, shortening the sarcomere.
Sarcoplasmic reticulum
The smooth ER of a muscle cell, enlarged and specialized to act as a Ca2+ reservoir. The SR winds around each myofibril in the muscle cell.
Schwann cell
One of the two peripheral nervous system supporting (glial) cells. Schwann cells from he myelin sheath on axons of peripheral neurons.
Sclera
The white portion of teh tough outer layer of the eyeball
Sebaceous gland
Oil-forming glands found all over the body, especially on the face and neck. The product (sebum) is released to the skin surface through hair follicles.
Seondary active transport
Active transport that releies on an established concentration gradient, typically set up by a primary active transporter. Secondary active transport relies on ATP indirectly.
Secondary immune response
A subsequent immune response to previously encountered antigen that results in antibody production and T cell activation. The secondary immune response is mediated by memory cells (produced during the primary immune respone) and is much faster and stronger than the rpimary response, typicaly taking only a dya or less. THis is not long enough for the infection to become established, and symptoms do not appear, thus the person is said to be "immune" to that particular antigen.
Secondary oocyte
A haploid cell resulting from the first meiotic division of oogenesi (not that the cytoplasmic division in this case is unequal, producing one large cell with almost all of they cytoplasm - the secondary oocyte- and one smaller cell with virtually no cytoplasm - the first polar body.). The secondary oocyte (along with some follicular cells) is released from the ovary during ovulation.
Secondary spermatocytes
Haploid cells resulting from the first meiotic division of spermatogenesis. Secondary spermatocytes are ready to enter meiosis II.
Secondary sex characteristics
The set of adult characteristics that develop during puberty under the control of the sex steroids. In males the secondary sex characteristics include enlargement and maturation of the genitalia, growth of facial, body, and pubic hair, increased muscle mass, and lowering of the voice. In females, the characteristics include the onset of menstruation and the menstrual cycle, enlargement of the breasts, widening of the pelvis, and growth of pubic hair.
Second Law of Thermodynamics
The entropy (disorder) of the universe (or system) tends to increase.
Second messenger
An intracellular chemical signal (such as cAMP ) that relays instructions from the cell surface to enzymes in the cytosol.
Secretin
A hormone secreted by the small intestine (duodenum) in response to low pH (e.g., from stomach acid). It promotes the release of bicarbonate from the pancreas to act as a buffer.
Secretion
(1) The secretion of useful substances from a cell, either into the blood (endocrine secretin) or into a cavity or onto the body surface (exocrine secretion). (2) in the nephron, the movement of substances from the blood to the filtrate along the tubule. Secretion increases the rate at which substances can be removed from the body.
Secretory phase
The third phase of the uterin (endometrial) cycle, during which the rebuilt endometrium is enhanced with glycogen and lipid stores. The secretory phase is primarily under the controll of progestone and estrogen (secreted from the copus luteum during this time period), adn typically lasts from day 15 to day 28 of the menstrual cycle.
Semen
An alkaline, fructose-rich fluid produced by three different glands in the male reproductive tract and released during ejaculation. Semen is very nourishing for sperm.
Semicircular canals
Three loop-like structures in the inner ear that contain sensory receptors to monitor balance.
Semiconservative replication
DNA replication in which each of the parental strands is read to make a complementary daughter strand, ethus each new DNa molecule is composed of half the parental molecule paired with a newly synthesized strand.
Semilunar valves
The valves in the heart that separate the ventricles from the arteries. The pulmonary semilunar valve separates the right ventricle from the pulmonary artery, and the aortic semilunar valve separates left ventricle from the aorta. These valves close at the end of systole, preventing the backflow of blood from arteries to ventricles, and producing the second heart sound.
Seminal vesicles
Paired glands found on the posterior external wall of the bladder in males. Their secretions contain an alkaline mucus and fructose, among other things, and make up approximately 60% of the ejaculate volume.
Seminiferous tubules
Small convoluted tubules in the testes where spermatogenesis takes place.
Sertolli cells
Cells that form the walls of the seminiferous tubules and help in spermatogenesis Sertoli cells are also called susenacular cells.
Serum
Plasma with the clotting factors removed. Serum is often used in diagnostic tests because it does not clot.
Sex-linked rait
A triat determined by a gen on either the X or Y chromosomes (the sex chromosomes).
Shine-Dalgarno sequence
The prokaryotic ribosome-binding site on mRNA, found 10 nucleotides 5' to the start codon.
Signal recognition particle (SRP)
A cytoplasmic protein that recognizes the signal sequences of proteins destined to be translated at the rough ER. It binds first to the ribosome translating the protein with the signal sequence then to an SRP receptor on the rough ER>
Signal sequence
A short sequence of amino aids, usually found at the N-terminus of a protein being translated, that directs the ribosome and its associated mRNa to the membranes of the rough ER where trasnlation will be completed. Signal sequences are found on membrane-boudn proteins, secreted proteins, and proteins destined for other organelles.
Signal transduction
The intracellular process triggered by the binding of a ligand to its receptor on the cell surface. Typically this activates seond messenger pathways.
Silent mutation
A point mutation in which a codon that specifies an amino acid is mutated into a new codon that specifies the same amion acid.
Simple diffsuion
The movement of a hydrophobic molecule across the plasma membrane of cell, down its concentration gradient. Since the molecule can esialy interact with the lipid bilayer, no additional help (such as a channel or pore) is required.
Single strand binding proteins
Proteins that bind to and stabilize the signle strands of DNA exposed when helicase unwinds the double helix in preparation for replication.
Sinoatrial (SA) node
A region of specialized cardiac muscle cells in the right atrium of the heart that initiate the impules of heart contraction; for this reason the SA node is knownas the 'pacemaker' of the heart.
Sister chromatid
Identical copies of a chromosome, produced during DNA replication and held together at the centromere Sister chromatids are separated during anaphase of mitosis.
Skeletal muscle
Muscle tissue that is attached to the bones. SKeletal muscle is striated multinucleate, and under voluntary control.
Siding filament theory
The mechanism of contraction in skeletal and cardiac muscl cells. It is a series of four repeated steps: (1) myosin binds actin, (2) myosin pull actin toward the center of the sarcomere (3) myosin releases actin, and (4) myosin resets to its high-energy conformation.
Slow block to polyspermy
Also known as the cortical reaction, the slow block invovles an increase in intracellular [Ca2+] in the egg, which causes the release of cortical granules near the egg plasma membrane. This results in the hardening of the zona pellucida and its separation from the surface of the egg, preventing the entry of more than one sperm into the egg.
Small intestine
The regino of the digestive tract where virtually al digestion and absorption occur. It is subdivided into three regions: the duodenum, the jejunum, and the ileum.
Smooth Endoplasmic Reticulum
A network of membranes inside eukarytoic cells invovled in lipid synthesis (steroid in gonads), detoxification (in liver cells), and/or Ca2+ storage (muscle cells).
Smooth muscle
Muscle tissue found in the walls of hollow organs, e.g., blood vessels, the digestive tract, the uterus, etc. Smooth muscle is non-striated, uninucleate, and under involuntary control (controlled by the autonomic nervous system).
Soma
The cell body of a neuron.
Somatic nervous system
The division of the peripheral nervous system that innervates and controls the skeletal muscles; also known as the voluntary nervous system.
Spatial summation
Integration by a postsynaptic neuron of inputs (EPSPs and IPSPs) from multiple sources.
Spermatid
A haploid but immature cell resulting from the second meiotic division f spermatogenesis. Spermatids undergo significant physical changes to become mature sperm (spermatozoa).
Spermatogenesis
Sperm production; occurs in human males on a daily basis from puberty until death. Spermatogenesis results in the production of four mature gametes (sperm) from a single precursor cell (spermatogonium). For maximum sperm viability, spermatogenesis requires cooler temperatures and adequate testosterone.
Spermatogonium
A diploid cell that can undergo mitosis to form more spermatogonium, and can also be triggered to undergo meiosis to form sperm.
S phase
The phase of the cell cycle during which the genome is replicated.
Sphincter of Oddi
The valvecontrolling release of bile and pancreatic juice into the bloodstream.
Sphygmomanometer
A blood pressure cuff
Spirochete
A bacterium having a spiral shape (plural = spirochetes)
Spleen
An abdominal organ that is considered part of the immune system. THe spleen has four functions: (1) it filters antigen from the blood (2) it is the site of B cell maturation, (3) it stors blood, and (4) it destroys old red blood cells.
Splicing
One type of eukaryotic mRNA processing in which introns are removed from the primary transcript and exons are ligated together. SPlicing of transcripts can be different in different tissues.
Spongy bone
A looser, more porous type of bone tissue found at the inner core of the epiphyses in long bones and all other bone types. Spongy gone is filed with red bone marrow, important in blood cell formation.
Start site
The location on a chromosome where transcription begins.
Steroid hormone
A hormone derived from cholesterol. Steroids are generally hydrophobic and can easily cross the plasma membrane of cells, thus receptors for steroids are found intracellularly. Once this steroid binds to its receptor, the receptor-steroid complex acts to regulate transcription in the nucleus.
Stomach
The portion of the digestive tract that stores and grinds food. Limited digestion occurs in the somach, and it has the lowest pH in the body (1-2).
Stop codon
A group of nucleotides that does not specify a particular amino acid, but instead serves to notify the ribosome that the protein being translated is complete. The stop codons are UAA, UGA, and UAG. They are also known as nonsense codons.
Stroke volume
The volume of blood pumped out the heart in a single contraction.
Submucosa
The layer of connective tissue directly under the mucosa of an open body cavity.
Substrate(s)
The reactants in an enzyme-catalyzed reaction. Substrate binds at the active site of an enzyme.
Sudoriferous gland
A sweat gland located in the dermis of the skin. Sweat consists of water and ions (including Na+ and urea) and is secreted with temperatures rise.
Summation
(1) The integration of input (EPSPs and IPSPs) from many presynaptic neruons by a single postsynaptic neuron, either temporaly or spatially. Summation of al input can either stimulate the postsynaptic neuron and possibly lead to an action potential, or it can inhibit the neuron, reducing the likelihood of an action potential. (2) The integration of single muscle twitches into a sustained contraction (tetany).
Supercoiling
A method of DNA protection utilized by prokaryotes in which their large circular chromosome is coiled upon itself.
Surfactant
An amphipathic molecule secreted by cells in the alveoli (type 2 alveolar cells) tha reducs surface tension on the inside of the alveolar walls. This prevents the alveoli from collapsing upon exhale and sticking together, thus reducing the effort required for inspiration.
Sympathic nervous system
The division of the autonomic nervous system known as the "fright or flight" system. It causes a genera increase in body activities such as heart rate, respiratory rate, and blood pressure, and an increase in blood flow to skeleltal muscle. It causes a general decrease in digestive activity. Because al of its preganglionic neurons originate from the thoraci or lumbar regions of the spinal cord, it is also known as the thoracolumbar system.
Symporter
A carrier protein that transports two molecules across the plasma membrane in the same direction. For example, the Na+-glucose cotransporter in intestinal cells is a symporter.
Synapse
A neuron-to-neuron, neuron-to-organ, or muscle to cell-to-muscle cell junction.
Synapsis
Pairing of homologus chromosomes in a diploid cell, as occurs during prophase I of meiosis.
Synaptic cleft
A microscopic space between the axon of one neuron and the cell body or dendrites of a secon neruon, or between the axon of a neuron and an organ.
Syncytium
A large multinucleate cell, typically formed by the fusion of many smaller cells during development (e.g. a skeletal muscle cell), or formed by nuclear division in the absence of cellular division.
Syngergist
Something that works together with another thing to augment the the second thing's activity. For example, a uscle that assists another muslce is said to be a syngergist. An enzyme that helps another enzyme is a synergist.
Synovial fluid
A lubricating, nourishing fluid found in joint capsules.
Systemic circulation
The flow of blood from the heart, through the body (not including the lungs), and back to the heart.
Systole
The period of time during which the ventricles of the heart are contracted.
Systolic pressure
The pressure measured in the arteries during contraction of the ventricles (during systole).
T cell
A type of lymphocyte. The major subtypes of T cells are the helper T cells (CD4) and the killer T cells (CD8, or cytotoxic T cells). Helper T cells secrete chemicals that help killer Ts and B cells proliferate. Killer T cells destroy abnormal self-cells (e.g., cancer cells) or infected cells.
Telencephalon
The cerebral hemispheres.
Telomere
A specialized region at the ends of eukaryotic chromosmes that contains several repeats of a particular DNA sequence. These ends are maintained (in some cells) with the help of a special DNA poymerase called telomerase. In cells that lack telomerase, the telomeres slowly degrade with each round of DNA replication (as the RNA primer, is not replaced and the 5' of the new DNA would not exist); this is though to contribute to the eventual death of the cell.
Telophase
The fourth (and final) phase of mitosis. During telophase the nuclear envelope reforms, chromosomes decondense, and the mitotic spindle is disassembled.
Telophase I
The fourth of meiosis I. Telophase I is identical to mitotic telophase, except that the number of chromosoms is now reduced by half. After this phase the cell is considered to be haploid. Note however, that the chromosomes are still replicated, and the sister chromatids must still be separated during meiosis II.
Telophase II
The fourth and final phase of meiosis II. Telophase II is identical to mitotic telophase, except that the number of chromosomes was reduced by half during meiosis. I.
Temporal summation
Summation by a postsynaptic cell of input (EPSPs or IPSPs) from a single source over time.
Tendon
Strong bands of connective tissue that connect skeletal muscle to bone.
Testcross
A genetic cross between an organism displaying a recessive phenotype (homozygous recessive) and an organism displaying a dominant phenotype (for whic the genotype is unknown), done to determine the unknown genotype.
Testes
The primary male sex organ. The testes are suspended outside the body cavity in the scrotum and have two functions (1) produce sperm, and (2) secrete testosterone.
Testosterone
The primary androgen (male sex steroid). Testosterone is a steroid hormone produced and secreted by the interstitial cells of the testes. It triggers the development of secondary male sex characteristics during puberty (including spermatogenesis) and maintains those characteristics during adulthood.
Tetanus
A smooth sustained muscle contraction, such as occurs in skeletal muscle when stimulation frequency is high enough (this is the normal type of contraction exhibited by skeletal muscle).
Tetrad
A pair of replicated homologous chromosomes. Tetrads form during prophase I of meiosis so that homologous chromosomes can exchange DNA in a process known as 'crossing over.'
Thalamus
The central structure of the diencephalon of the brain. the thalamus acts as a relay station and major integrating area for sensory impulses.
Thecal cells
A layer of cells surroudning the granulosa cells of the follicles in an ovary. Thecal cells help produce the estrogen secreted from the follicle during the first phase of the ovarian cycle.
Thermoreceptor
A receptor that responds to changes in temperature.
Theta replication
DNA replication in prokaryotes, so named because as replication proceeds around the single, circular chromosome, it takes on the appearnce of the Greek letter theta.
Thick filament
In skeletal and cardiac muscle tissue, a filament composed of bundles of myosin molecules. The myosin head groups attach to the thick filaments and pull the toward the center of the sarcomere during muscle contraction.
Thin filament
In skeleta and cardiac muscle tissue, a filament composed of actin, tropomyosin, and troponin. Thin filaments are attached to teh Z lines of the sarcomers and slide over thick filaments during muscle contraction.
Thrombus
A blood clot that forms in an unbrokened blood vessel. Thrombi are dangerous they can break free and begin travelin in the bloodstream (become an embolus). Emboli ultimately become stuck in a small vessel and prevent adequate blood delivery to tissues beyond the sticking point, leading to tissue death. A brain embolism cna lead to stroke, a heart embolism to a heart attack, and a pulmonary embolism to respiratory failure.
Thymine
One of the four aromatic bases found in DNA. Thymine is a pyrimidine; it pairs with adenine.
Thymus
An immune organ located near the heart. THe thymus is the site of T cell maturation and is larger in children and adolescents.
Thyroid stimulating hormone (TSH)
A tropic hormone produced by the anterior pituitary gland that targets the thyroid gland, stimulating it to produce and release thyroid hormone.
Thyroxine
Also called thryoid hormone, thyroxine is produced and secreted by follicle cells in the thyroid gland. it targets all cells in the body and increases overall body metabolism.
Tidal volume
The volume of air inhaled and exhaled in a normla, resting breath, typically about 500 mL.
Tight junction
Also called occluding junctions, tight junctions form a seal between cells that prevents the movement of substances across the cell layer, except by diffusion through the cell membranes themselves. Tight junctions are found between the epithelial cells lining the intestines and between the cells forming the capillaries in the brain (the blood-brain barrier).
Tolerant anaerobe
An organism that can survive in the presence of oxygen (oxygen is not toxic), but that does not use oxygen during metabolism (anaerobic metabolism only).
Tonsils
Paired masses of lymphatic tissue near the back of the throat that help trap inhaled or swallowed pathogens.
Topoisomerase
An enzyme that cuts one or both strands of DNa to relieve the excess tension caused by the unwinding of the helix by helicase during replication.
Total lung capacity
The maximal volume of air that the lungs can contain. Total lung capacity is the sum of the vital capacity and the residual volume, and is typically about 6000 mL (6L).
Totipotent
Having the ability to become anything; a zygote is totipotent.
Trachea
The main air tube leading into the respiratory system. The trachea is made of alternating rings of cartilage and connective tissue.
Transcription
The enzymatic process of reading a strand of DNA to produce a complemenetary strand of RNA
Transduction
The transfre by a lysogenic virus of a portion of a host cell genome to a new host.
Transition mutation
A point mutation in which a pyrimidine is susbstituted for a pyrimidine, or a purine is substituted for a purine.
Translation
The process of reading a strand of mRNA to synthesize protein. Protein translation takes place on a ribosome.
Transmembrane domain
The portion of an integral membrane protein that passes through the lipid bilayer.
Transversion mutation
A point mutation in which a pyrimidine is substitued for a purine, or vice versa.
tRNA
Transfer RNA; the type of RNA that carries an amino acid from the cytoplasm to the ribosome for incorporation into a growing protein.
tRNA loading
The attachment of an amino acid to a tRNA (not that this a specific interaction). tRNa loading requires two high-energy phosphate bonds.
Trophoblast
The outer ring of cells of a blastocyst. The trophoblast takes part in the formation of the placenta.
Tropic hormone
A hormone tha tcontrols the release of another hormone.
Tropomyosin
A helical protein that winds around actin helices in skeletal and cardiac muscle cells to form the thin filament of the sarcomere. In the absence of Ca2+, tropomyosin covers the myosin-binding sites on actin and prevents muscle contraction. When calcium is present, a conformation change in tropomyosin occurs so that the myosin-binding sites are exposed and muscle contraction can occur.
Troponin
A globular protein that ssociated with tropomyosin as part of the thin filament of the sarcomere. Troponin binds Ca2+, which causes the conformaiton change in tropomyosin required to expose the myosin-binding sites on actin and initiate muscle contraction.
Trypsin
The main protease secreted by the pancreas; trypsin is activated (from trypsinogen) by enterokinase, and subsequently activates other pancreatic enzymes.
T tubules
Also called transverse tubules, these are deep invaginations of the plasma membrane found in skeletal and cardiac muscle cells. These invaginations allow depolarization of the membrane to quickly penetrate to the interior of the cell.
Tympanic membrane
The membrane that separate the outer ear from the middle ear. The tympanic membrane is also known as the eardrum.
Umbilical cord
The cord that connects the embryo of a developing mammal to the placenta in the uterus of the mother. The umbilical cord contains fetal arteries (carry blood toward the placenta) and veins (carry blood away from the placenta). The umbilical vessels derive from the allantois, a structure that develops from the embryonic gut.
Uniporter
A carrier protein that transports a single molecule across the plasma membrane.
Universal acceptor
A person with blood type AB+. Because this person's red blood cells possess all of the typical blood surface proteins, they will not display an immune reaction if transfused with any of the other blood types.
Universal donor
A person with blood type O-. Because this person's red blood cells possess none of the typical blood suface proteins, they cannot initiate an immune reaction in a recipient.
Upsteam
Toward the 5' end of an Rna transcript (the 5' end of the DNA coding strand). The promoter and start sites are upstream.
Uracil
One of the four aromatic bases found in RNA. Uracil is pyrimidine; it pairs with adnenine.
Urea
A waste product of protein dbreakdown, produced by the liver and relased into the bloodstream to be eliminated by the kidney.
Ureters
The tubes that carry urine from the kindeys to the bladder.
Urethra
The tube that carries urine from the bladder to the to outside of the body. In males it also carries semen and sperm during ejaculation.
Urinary sphincter
The valve that controls the release of urine from the bladder. It has an internal part made of smooth muscle (thus involuntary) and an external part made of skeletal muscle (thus voluntary).
Uterine tubes
Also called falopian tubes, these tubes extend laterally from their side of the uterus and serve as a passageway for the ocyte to travel from the ovary to the uterus. This is also the normal site of fertilization. Severing of the uterine tubes (tubal ligation) results in sterility of the femlae.
Uterus
The muscular femal organ, in which a baby develops during pregnancy.
Vaccination
The deliberate exposure of a person to an antigen in order to provoke the primary immune response and memory cell production. Typically the antigens are those normally associated with pathogens, thus if the live pathogen is encountered in the future, the seconday immune response can be initiated, preventing infection and symptoms.
Vagal tone
The constant inhibition provided to the heart by the vagus nerve. Vagal tone reduces the intrinsic firing rate of teh SA node from 120 beats/minute to around 80 beats/minute.
Vagina
The birth canal; the stretchy, muscular passageway through which a baby exits the uterus during childbirth.
Vagus nerves
Cranial nerve pair X. The vagus nerves are very large mixed nerves (They carry both sensory input and motor input) that innervate virtually every visceral organ. They are especially important in transmitting parasympathetic input to the heart and digestive smooth muscle.
Vasa recta
The capillaries that surround the tubules of the nephron. The vasa recta reclaims reabsorbed substances, such as water and sodium ions.
Vas deferens
A thick muscular tube that connects the epididymis of the testes to the urethra. Muscular contractions of the vas deferns during ejaculation ehp propel the sperm outward. Severing of the vas deferens (vasectomy) results in sterility of the male.
Vein
A blood vessel that carries blood toward the heart chambers. Veins do not have muscular walls, have valves to ensure that blood flows in one direction only, and are typically low-pressure vessels.
Vena cava
One of two large vessels (superior and inferior) that return deoxygenated blood to the right atrium of the heart.
Venous returns
The amount of blood returned to heart by the vena cavae.
Ventricle
One of two large chambers in the heart. The ventricles receive blood from the atria and pump it out of the lungs of the heart. The right ventricle has thing walls and pumps deoxygenated blood to the lungs through the pulmonary artery. The left ventricle has thick walls and pumps deoxygenated blood the body through the aorta.
Vestibular glands
Paired glands near the posterior side of the vaginal that secrete an alkaline mucus upon sexual arousal. The mucus helps to reduce the acidity of the vagina (which could be harmful to sperm) and lubricates the vagina to facilitate penetration.
Villi
(Singular:villus). Folds of the intestinal mucosa that project into the lumen of the intestine; vili serve to increase the surface area of the intestine for absorption.
Virus
A nonliving, intracellular parasite. Viruses are typically just pieces of nucleic aid surrounded by a protein coat.
Vital capacity
The maximum amount of air that can be forcibly exhaled from the lungs after filling them to their maximum level, typically about 4500 mL
Vitamin
One of several different nutrietns that must be consumed in the diet, and generally not synthesized in the body. Vitamins can be hdyrophobic (fat-solube) or hydrophilic (water-soluble).
Vitreous humor
A thick, gelatinous fluid found in the posterior segment of the eye (between the lens and the retina). The vireous humor is only produced during fetal development and helps maintain intraocular pressure (the pressure inside the eyeball).
Voltage-gated ion channel
An ion channel that is oepend or closed based on the electrical potential across the plasma membrane. Once opened, the channel allows ions to cross the membrane according to their concentration gradients. Examples are the Na+ and K+ voltage-gated channels involved in the action potential of neurons.
White matter
Myelinated axons
Wolffian ducts
Early embryonic ducts that can develop into male internal genitalia under the proper stimulation (testosterone).
Yolk sac
An embryonic structure particularly important in egg-laying animals because it contains the yolk, the only source of nutrients for the embryo developing inside the egg. IN humans, the yolk sac is very small (since mammals get their nutrients via the placenta) and is the site of synthesis of the first red blood cells.
Z lines
The ends of a saromere.
Zona pellucida
A thick, transpartent coating rich in glycoproteins that surrounds an oocyte.
Zygote
A diploid cell formed by the fusion of two gametes during sexual reproduction.
Zymogen
An inactive precursor of an enzyme, activated by various methods (acid hydrolysis, cleavage by another enzyme, etc.)
Releasing and Inhibiting Factors
HYPOTHALAMUS -> ANTERIOR PITUITARY: modifies activities
Growth Hormone
ANTERIOR PITUITARY: increases bone and muscle growth, increases cell turnover rate
Prolactin
ANTERIOR PITUITARY -> MAMMARY GLAND: milk production
Thyroid Stimulating hormone
ANTERIOR PITUITARY -> THYROID: increases synthesis and release of thyroid hormone (tropic)
Adrenocorticotropic hormone
ANTERIOR PITUITARY -> ADRENAL GLAND: increases growth and secretory activity of adrenal cortex
Luteinizing hormone
ANTERIOR PITUITARY -> OVARY/ TESTES: ovulation or testosterone synthesis
Follicle Stimulating hormone
ANTERIOR PITUITARY -> OVARY / TESTES: follicle development or spermatogenesis
Antidiuretic hormone
POSTERIOR PITUITARY -> KIDNEY: water retention (Vasopressin)
Oxytocin
POSTERIOR PITUITARY -> BREAST & UTERUS: milk letdown and uteral contractions
Thyroid hormone
THYROID: in the child it is necessary for physical and mental development; in the adult, it increases metabolic rate and temperature
Calcitonin
THYROID C CELLS -> BONE, KIDNEY, SMALL INTESTINE: lowers serum [Ca2+]
Parathyroid hormone
PARATHYROIDS -> BONE, KIDNEY, SMALL INTESTINE: raises serum [Ca2+]
Thymosin
THYMUS: is involved in T-cell development during childhood.
Epinephrine
ADRENAL MEDULLA: sympathetic stress response (rapid)
Cortisol
ADRENAL CORTEX: results in a longer-term stress response; increased blood [glucose]; increased protein catabolism; decreased inflammation and immunity; many other (glucocorticoid)
Aldosterone
ADRENAL MEDULLA -> KIDNEY: increased Na+ reabsorption to increase blood pressure
Sex steroids
ADRENAL CORTEX: not normally important, but an adrenal tumor can overproduce these, causing masculinization or feminization.
Insulin
BETA CELLS OF THE ISLETS OF LANGERHANS IN THE PANCREAS: decreases blood [glucose]; increases glycogen and fat storage; it is activated at high blood [glucose] and is absent or ineffective in diabetes melitus
Glucagon
ALPHA CELLS OF THE ISLETS OF LANGERHANS IN THE PANCREAS: secreted at low blood [glucose] and results in an increase in blood [glucose] and decrease in glycogen and fat storage
Somatostatin
SIGMA CELLS OF THE ISLETS OF LANGERHANS IN THE PANCREAS: inhibits many digestive processes
Testosterone
TESTES: male characteristics; spermatogenesis
Estrogen
OVARIES / PLACENTA: Female characteristics, endometrial growth
Progesterone
OVARIES / PLACENTA: leads to endometrial secretion, pregnancy
Atrial natriuretic factor
HEART -> KIDNEY: increases urination to decrease blood pressure
Erythropoeitin
KIDNEY -> BONE MARROW: increases RBC synthesis
Regulation of Ca
Parathyroid hormone and Calcitonin
Regulation of blood glucose
Insulin and Glucagon
Milk production and letdown
Oxytocin and Prolactin
Pancreas
[Location] Glucagon (alpha) & Insulin (beta) & Somatostatin (sigma)
Blood Pressure
Atrial natriuretic factor (ANF) & Aldosterone Regulates....
Blood Glucose
Glucagon (polypeptide derivative), Epinepherine (amino acid derivative), Cortisol (steroid / glucocorticoid) Regulates...