MCAT Biology Anatomy Flashcards

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5' cap

a methylated guanine nucleotide added to the 5' end of eukaryotic mRNA. The cap is necessary to initiate translation of mRNA

Acetylcholine (Ach)

The neurotransmitter used throughout the parasympathetic nervous system as well as the neuromuscular junction.

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

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.

Adrenergic tone

A constant input to the arteries that keeps them somewhat constricted to maintain a basal level of blood 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).

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.

Amylase

An enzyme that digests starch into disaccharides. Amylase is secreted by salivary glands and by the pancreas.

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.

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.

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"

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

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.

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.

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)

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.

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.

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.

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).

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.

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.

Catalase

The primary enzyme in peroxisomes; catalse catalyzes the hydrolysis of hydrogen peroxide (H2O2) into water and oxygen.

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.

Cerebellum

The region of teh brain that coordinates and smooth skeletal muscle activity.

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'.

Chief cells

Pepsinogen-secreting cells foudn at teh bottom of the gastric glands

Chorion

The portion of the placenta derived from the zygote.

Chymotrypsin

One of the main pancreatic proteases; it is activated (from chymotrypsinogen) by trypsin.

Cleavage

The rapid mitotic division of a zygot that being within 24-36 hours after fertilization

Coenzyme

An **organic molecuel taht associates non-covalently with an enzyme, and that is required for the proper functioning of the enzyme.

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.

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.

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.

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.

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.

Depolarization

The movement of teh membrane potential of a cell away from rest potential in a more positive direction.

Diaphysis

The shaft of a long bone. The diaphysis is hollow and is made entirely from compact bone.

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).

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.

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.

Efferent neuron

A neuron that carries information (action potentials) away from the central nervous system; a motor neuron.

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.

Endocytosis

The uptake of material into a cell, usually by invagination. See also 'phagocytosis', pinocytosis, and receptor-mediated endocytosis..

Endosymbitoic theory

the theory that mitochondria and chloroplasts originated as independent unicellular organsims living in symbiosis with larger cells

Enterokinase

A duodenal enzyme that activates trypsinogen (from the pancreas) to trypsin.

Epiglottis

A flexible piece of cartilage in the larynx that flips downward to seal teh trachea during swallowing.

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.)

Erythropoietin

A hormone produced and released by the kidney that stimulates the production of red blood cells by the bone marrow.

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.

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).

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'.

Fascicle

A bundle of skeletal muscle cells. Fascicles group together to form skeletal muscles.

Fimbriae

Fingerlike projection of the uterin (fallopian) tubes that drape over the ovary.

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).

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.

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.

Gene pool

The sum of all genetic material in a population.

Glomerulus

The ball of capillaries at the beginning of the nephron where blood filtration takes place.

Gonadotropin releasing hormone (GnRH

A hormone released from the hypothalamus that triggers the anterior pituitary to secrete FSH and LH.

Gram-positive bacteria

Bacteria that have a thick peptido glycan cell wall, and no outer membrane. They stain very darkly (purple) in Gram stain.

Gustatory receptors

Chemoreceptors on the tongue that respond to chemicals in a food.

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.

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.

Heterotroph

An organism that cannot make its own food, and thus must ingest other organisms.

hnRNA

Heterogeneous nuclear RNA; the primary transcript made in eukaryotes before splicing.

Humoral immunity

Specif ic defense of the body by antibodies, secreted into the blood by B-cells.

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.

Ileum

The final section (approximately 55%) of the small intestine.

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).

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).

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.

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.

Jejunum

The middle (approximtely 40%) of the small intestine.

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)

Lacunae

Small cavities in the bone or cartilage that hold individual bones or cartilage cells.

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).

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.

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.

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.

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.

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.

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.

Maternal inheritance

Genes that are inherited only from the mother, such as mitochondrial genes (all organelles come only from the ovum).

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.

Menopause

The perio dof tim ein a woman's life when ovulation and menstruation cease. Menopause typically begins in the late 40s.

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.

Midbrain

The portion of the brain responsible for visual and auditory startle reflexes.

Monocistronic mRNA

mRNA that codes forsingle type of protein, such as is found in eukaryotic cells.

Motor unit recruitment

A mechanism for increasing tension (contractile length) in a muscle by activating more motor units.

Mullerian inhibiting factor (MIF)

A substance secreted by embryonic testes that causes the regression of the Mullerian ducts.

Myofibril

A string of sarcomeres with a skeletal muscle cell (hence smaller than myofiber). Each muscle cell contains hundreds of myofibirils.

NADH

The reduced form of NAD+ (nicotinamide adenine dinucleotide). This is the most common electron carrier in cellular respiration.

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.

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

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.

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.

Okazaki fragments

Small fragments of DNa produced on the lagging strand during DNa replication, joined later by DNA ligase to form a complete strand.

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.

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.

Osteoblast

A cell that produces bone.

Oval window

The membrane that separates the middle ear from the inner ear.

Oxidation

To attach oxygen, to remove hydrogen, or to remove electrons from a molecule.

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).

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.

Peptide bond

The bond formed between the carboxyl group of one amino acid and the amino group of another.

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.

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.

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.

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.

Plasmid

A small, extrachromosomal (outside the genome), circular DNA molecule found in prokaryotes.

Point mutation

A type of mutation in DNa where a single base is substituted for another.

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.

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.

Primary bronchi

The first branches of the trachea. There are two primary bronchi, one for each lung.

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.

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.

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.

Ptyalin

Salivary amylase

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.

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.

Rectum

The final portion of the large intestine.

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.

Replication bubbles

Multiple sites of replication found on large, linear eukaryotic linear eukaryotie chromosomes.

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.

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.

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.

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.

S phase

The phase of the cell cycle during which the genome is replicated.

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.

Second Law of Thermodynamics

The entropy (disorder) of the universe (or system) tends to increase.

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.

Seminiferous tubules

Small convoluted tubules in the testes where spermatogenesis takes place.

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.

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>

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.

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.

Somatic nervous system

The division of the peripheral nervous system that innervates and controls the skeletal muscles; also known as the voluntary nervous system.

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.

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.

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).

Synapse

A neuron-to-neuron, neuron-to-organ, or muscle to cell-to-muscle cell junction.

Synovial fluid

A lubricating, nourishing fluid found in joint capsules.

Telencephalon

The cerebral hemispheres.

Temporal summation

Summation by a postsynaptic cell of input (EPSPs or IPSPs) from a single source over time.

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).

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.

Thymus

An immune organ located near the heart. THe thymus is the site of T cell maturation and is larger in children and adolescents.

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).

Trachea

The main air tube leading into the respiratory system. The trachea is made of alternating rings of cartilage and connective tissue.

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