Study sets, textbooks, questions
Upgrade to remove ads
Cell Physiology - Guyton
Terms in this set (152)
Label a neuromuscular junction
What neurotransmitter excites muscle?
What is the purpose of opening Ach channels in muscle fibers?
Pours in positive sodium ions into the fiber that carry positive charge (end plate potential), which spreads the AP along the muscle membrane to cause a contraction.
How is Ach removed from the synaptic space?
1. destruction by acetylcholinesterase***
2. Diffusion out of the synaptic space
Where is Ach synthesized?
Cytoplasm of the nerve fiber terminal
What drugs have acetylcholine like activity?
What drugs inactivate acetylcholinesterase?
What drugs block transmission at the neuromuscular junction?
Curariform drugs (d-tubocurarine)
How does myasthenia gravis affect the muscles ?
Inability of the neuromuscular junction to transmit enough signals from the nerve fibers to the muscle fibers.
Antibodies that attack the acetylcholine receptors
How does a nerve impulse get from the surface membrane into the muscle fibers?
Along the transverse tubules (T tubules, open to ECF) to cause release of calcium ions inside the muscle fiber (excitation contraction coupling)
Describe excitation contraction coupling?
What does smooth muscle not possess that is in abundance in skeletal muscle?
What replaces troponin in smooth muscle cells?
Calmodulin (activates myosin cross-bridges)
How does calmodulin initiate muscular contraction?
1. calcium concentration in the cytosolic fluid of smooth muscle increases due to influx of calcium from the ECF
2. Calcium ions bind reversibly to calmodulin
3. Calmodulin-calcium complex joins up and activates myosin-light chain kinase
4. This phosphorylates the light chains of each myosin head., which can then bind repetitively with the actin filament and cycle through contraction
Where do the calcium ions come from for smooth muscle contraction?
Majority come from the ECF at the time of action potential or other stimulus. The sarcoplasmic reticulum is very underdeveloped.
What is required for smooth muscle relaxation?
Pumping of calcium ions from the smooth muscle fiber back into the ECF or the SR
What enzyme allows for reversal of the myosin head binding?
What makes up the neuromuscular junction of smooth muscle?
Autonomic nerve fibers that form diffuse junctions to secrete their neurotransmitters into the matrix coating of smooth muscle.
What is the excitatory neurotransmitter for smooth muscle?
Acetylcholine or NE
What is the inhibitory neurotransmitter for smooth muscle?
Norepinephrine or Ach
How are action potentials propagated at the neuromuscular junction?
1. Nerve impulse reaches terminal and opens calcium channels
2. Calcium-Calmodulin dependent protein kinase phosphorylates synapsin proteins
3. Frees Acetylcholine and allows exocytosis
4. Post-synaptic ion channels open and that allows Na influx and K efflux
5. Increases muscle membrane potential
What is multi-unit smooth muscle?
Separate smooth muscle fibers that operative independently and are innervated by 1 nerve
What is unitary smooth muscle?
Many fibers that operate as a single unit and are joined by gap junctions
How is smooth muscle organized?
Large numbers of actin filaments attached to dense bodies interspersed by thick myosin filaments
What is the general schema of genetic control? (steps to form proteins in the cell cytoplasm)
Gene (DNA) is transcribed to form RNA, which is then spliced to form mRNA, which is then transported to ribosomes, where it is translated and protein is formed.
What are the 6 different types of RNA?
1. Precursor messenger RNA (pre-mRNA)
2. Small nuclear RNA (snRNA)
3. Messenger RNA (mRNA)
4. Transfer RNA (tRNA)
5. Ribosomal RNA
6. Micro RNA (miRNA)
What is the function of precursor mRNA?
Large immature RNA strand that is processes in the nucleus to form mRNA
How is pre-mRNA modified to form mRNA?
Introns removed by splicing
Exons remain in the final mRNA
What is the function of snRNA?
Directs the splicing of pre-mRNA to mRNA
What is the function of tRNA?
Transports activated AAs to the ribosomes to be used in assembling the protein molecule
What is the function of ribosomal RNA?
Part of the ribosomes (along with other proteins)
What is the function of miRNA?
Regulation of gene transcription and translation
What is the function of mRNA?
Carries the genetic code to the cytoplasm for controlling the type of protein formed
What is the first step of cellular reproduction?
1. Replication of all DNA in the chromosomes
What are the phases of the cell cycle?
What enzymes are necessary for DNA replication?
1. DNA polymerase
2. DNA ligase
What are the phases of mitosis?
What is the function of telomeres?
Serve as protective caps that prevent the chromosome from deterioration during cell division
What role might telomeres play in disease?
Telomeres shorten every time DNA is replicated, which means there's only so many times a cell can divide. In cancer or proliferative diseases, telomerase activity (which adds bases to end of telomeres) is upregulated, meaning they are protected and can have unlimited division
Activation of what initiates the process of apoptosis?
Initiation of proteases that are called caspases which are stored as procaspases
What are the different types of diffusion?
1. Simple diffusion: Kinetic movement of molecules or ions occurs through a membrane opening or through intermolecular spaces without any interaction with carrier proteins
2. Facilitated diffusion: Requires interaction with carrier protein`
What allows water to pass through the cell membrane?
Aquaporins--single channel pore that allows water molecules to go through in single file, but is too narrow to permit passage of hydrated ions
What determines osmotic pressure?
The number of particles per unit volume of fluid. (which is equivalent to molar concentration if it is a nondissociated molecule)
What is one osmole?
1g molecular weight of osmotically active solute
What is primary active transport? Secondary active transport?
1: Primary: Energy derived from breakdown of ATP for transport.
2: Secondary: Energy derived from energy that has been stored in the form of ionic concentration differences of secondary molecular or ionic substances between the two sides of a cell membrane.
What controls protein synthesis?
RNA in the cytoplasm
How is RNA formed?
RNA polymerase attaches to a promoter, unwinds the DNA helix, makes a complementary RNA strand, synthesis of chain term seq, RNA chain separates
What is transfer RNA?
In ribosomes, each particular type of tRNA recognizes a codon on mRNA to deliver appropriate AAs to chain of forming protein molecules
Where does translation occur?
ribosomes in the cytoplasm
What are the processes involved in genetic regulation?
1. Promoter controls gene expression
2. Transcription is influenced by enhancers
3. Nuclear DNA is wound around histones and packaged as chromosomes
What happens in phase 1 of mitosis?
Prophase: While spindle is forming, chromosomes of the nucleus are condensed into chromatids
What happens in phase 2 of mitosis?
Prometaphase: Asters attach to chromatids and pull them toward the poles
What happens in phase 3 of mitosis?
Metaphase: Asters pushed further apart and chromatids line up at center to form equatorial plate
What happens in phase 4 of mitosis?
Anaphase: Chromatids pulled apart to make 46 pairs of daughter chromasomes and are pulled toward asters
What happens in phase 5 of mitosis?
Telophase: daughter chromosomes are pushed completely apart and new nuclear membrane forms
What are the most prevalent ions in the ECF?
What are the most prevalent ions in the ICF?
Low in sodium
What is the functional importance of Na-K-ATPase?
Important in controlling cellular volume
Interior cell has increased protein and organic molecules that are negative, attracting +Na/K
Membrane is less permeable to Na so once its pumped out, there is a net loss of + charge and net water out
Where does hydrogen active transport occur?
1. Parietal (oxyntic) cells of stomach
2. Intercalated cells in Late distal tubules/ collecting duct of kidney
What are examples of secondary active transport?
1. Co-transport of glucose/amino acids in intestinal epithelium/renal tubules
2. Na-Ca/H counter transport in proximal tubule of kidney
What equation describes the tendency for an ion to diffuse in one direction?
The nernst equation
What factors determine the diffusion potential of a membrane when the membrane is permeable to several different ions?
1. Polarity of the electrical charge of each ion
2. The permeability of the membrane to each ion
3. The concentrations of the respective ions on the inside and outside of the membrane
What are the most important ions involved in the development of membrane potentials in muscle and nerve cells?
Na, Cl, K
What are important factors in establishing a RMP of -90mV?
1. Only movement of ions through the membrane is diffusion of K+ via leak channels
2. Contribution of Na-K pump (pump more Na to outside than to the inside causes continual loss of positive charge, leading to additional degree of negativity)
What are the phases of an action potential?
1. Resting phase: RMP before AP begins. Membrane is said to be polarized during this stage
2. Depolarization: Membrane suddenly permeable to Na ions, allowing huge infkux of sodium into the interior of the axon.
3. Repolarization: Na channels close and K+ open. Rapid diffusion of K+ to the exterior to re-establish normal negative RMP
What causes activation of the sodium channel?
Slow leak potassium channels gradually take membrane potential upward. When it reaches a voltage of -70 to -50 mV it suddenly activates.
What causes inactivation of the sodium channel?
Within <second of activation, the huge influx of sodium ions leads to a conformational change that causes closure of the activation gate.
What is important to note about the inactivation of sodium channels?
The inactivation gate will not reopen until the membrane potential returns to or near the original RMP.
What causes activation of the potassium channel?
As membrane potential increases from -90mV, there is a conformational opening change of the gate that allows increased K+ diffusion outward through the channel. Slight delay then causes it to open just as sodium channels close due to inactivation, leading to increase in K+ exite.
Label an action potential.
What is the sodium to potassium conductance during an AP?
What types of voltage gated pumps are more numerous in cardiac or smooth muscle compared to skeletal muscle?
Calcium channel pumps
What direction do action potentials flow?
They have NO direction! The AP travels in all directions away from the stimulus until the entire membrane is depolarized.
How far does an AP go?
Depends on the membrane. If conditions are right, it travels over the entire membrane. If conditions aren't right then it doesn't travel at all. Therefore, it has an all-or-nothing principle
What causes a plateau in a AP?
1. Prolonged opening of slow Ca-Na channels allows calcium ions to enter the fiber
2. Voltage gated K+ channels are slower to open than usual, often not until the end of the plateau, which delays return to MP to negativity
What is the major reason for spontaneous rhythmicity to occur?
The membrane must be permeable to enough sodium ions (or calcium+sodium) to allow for automatic membrane depolarization.
What causes rhythmicity that is slightly delayed between depolarizations?
Potassium conductance currents that carry charge outside the membrane increasing negativity.
What deposits myelin around an axon?
What makes up the myelin?
Why is sphingomyelin good at electrical insulation?
Decrease ion flow through a membrane by 5000x
What is the function of a node of ranvier?
Allows ion flow in a myelinated axon, which allows for APs to occur at the NODES.
What is the principle of saltatory conduction?
APs are conducted from node to node
Why is saltatory conduction valuable?
Causes the depolarization to jump long intervals along the axis of the nerve fiber, therefore increases the velocity of nerve transmission in myelinated fibers 5-50x
Label a myofibril?
What are the thick filaments comprised of? Thin filaments?
2. Thin= actin
What are the light bands of a myofibril consisting of?
Called I bands (because they are isotropic to polarized light)
What are the dark bands of a myofibril consisting of?
Myosin filaments and the ends of actin filaments
A bands (anisotropic to polarized light)
What part of the myofibril is the cause of contraction?
Interaction between the cross bridges and actin filaments
What is the function of the Z disc?
Filamentous proteins that attaches myofibrils together
What is the portion of the myofibril that lies between two successive Z disks?
What acts as a framework to hold the myosin and actin filaments in place so the contractile machinery of the sarcomere will work?
What is the fluid that lies between myofibrils called? What is its composition?
Made up of K, Mg, PO, and protein enzymes
What are the steps of muscle contraction?
1. AP goes to the end of a motor nerve, which a small amount of ACh is secreted
2. Ach acts on local area of muscle fiber membrane to open Ach gated ion channels
3. This allows large quantities of sodium to diffuse intracellularly, which depolarizes the cell and opens voltage gated Na channels
4. AP travels along muscle fiber membrane just like a nerve
5.AP depolarizes the muscle membrane, where AP electricity goes to the sarcoplasmic reticulum to release calcium ions
6. Calcium ions initiate attractive forces between actin and myosin causing them to slide along eachother (contraction)
7. Calcium ions pumped back into SR, and remained stored until new AP comes along (ceasing contraction)
What makes up the troponin complex? What are their affinities?
1. Troponin I (actin affinity)
2. Troponin T (tropomyosin affinity)
3. Troponin C (calcium affinity)
Label an actin filament
What are the three sources of energy for muscle contraction?
2. Glycolysis of glycogen to pyruvic acid and lactic acid
3. oxidative metabolism**** (more than 95% of energy used by muscles is derived from this mechanism)
What are the characteristics of slow muscle fibers?
1. Smaller than fast fibers
2. Innervated by smaller nerve fibers
3. More extensive blood vessel system and more capillaries to supply extra amounts of oxygen
4. Increased numbers of mitrochondria to support high levels of oxidative metabolism
5. Large amounts of myoglobin
How does myoglobin improve muscle efficiency?
Combines with oxygen and stores it until its needed, which improves the speed of oxygen transport to the mitochondria
What are the characteristics of fast muscle fibers?
1. Larger=greater strength of contraction
2. Extensive sarcoplasmic reticulum for rapid release of calcium ions to initiate contraction
3. Large amounts of glycolytic enzymes present for rapid release of energy by glycolytic processes
4. Less extensive blood supply than slow fibers
5. Fewer mitochondria than slow fibers.
Why does tetany occur?
Enough calcium ions are maintained in the muscle sarcoplasm, even between action potentials, so the full contractile state is sustained without allowing any relaxation between APs
What is myosin composed of?
2 heavy chains
4 light chains
What is the "walk-along" theory of contraction?
When actin filament is activated by calcium ions, heads of cross-bridges from myosin filaments become attracted to active sites of the actin filament
Why is energy required for muscle contraction?
1. To pump calcium from sarcoplasm to sarcoplasmic reticulum after contraction
2. To pump sodium/potassium through the muscle fiber membranes
What is a motor unit?
A motor neuron and all of the muscle fibers it innervates
What are components of the extracellular fluid?
6. Fatty Acids
7. Amino Acids
8. Carbon Dioxide
What are components of the intracellular fluid?
What are the two stages of ECF transport throughout the body?
1. Movement of blood through the body in blood vessels
2. Movement of fluid between blood capillaries and intracellular spaces of tissue cells
How does diffusion occur?
Through the kinetic motion of the molecules in both the plasma and interstitial fluid
What are the different substances that make up a cell? What are they collectively called?
What are important ions in the cell?
K, Mg, P, Sulfate, Bicarb>>Na, Cl, Ca
What makes up 10-20% of cell mass?
What types of protein make up a cell?
1. Structural proteins
2. Functional proteins
What are some examples of structural proteins?
Microtubules to act as cytoskeletons of cellular organelles (cilia, nerve axons, mitotic spindles of cells undergoing mitosis)
Fibrillar proteins outside the cell (collagen and elastin fibers of CT)
What are examples of functional proteins of the cell?
What are the important lipids of the cell?
phospholipids and cholesterol
Draw the components of a cell
What composes a lipid bilayer?
phospholipids, sphingolipids, and cholesterol
What is the most abundant of the cell membrane lipids?
What part of the phospholipid is hydrophilic? hydrophobic?
Hydrophilic: Phosphate end
Hydrophobic: fatty acid portion
What are fat soluble substances?
Oxygen, CO2, and alcohol
What cell types have increased proportion of sphingolipids?
What are the two types of cell membrane proteins?
1. Integral proteins
2. Peripheral proteins
What are the three functions integral proteins can provide?
1. Carrier proteins
2. Receptors for water soluble chemicals (interaction with ligands to generate second messenger effect)
What function do peripheral proteins provide the cell?
Enzymes or as controllers of transport of substances
What do carbohydrates do in the cell membrane?
Combine with proteins or lipids in the form of glycoproteins or glycolipids
What functions do carbohydrates have that are attached to the outer surface of the cell? (4)
1. Negative charge to give overall cell surface negative charge.
2. Glycocalyces can attach to bind cells together
3. Act as receptor substances for binding hormones
4. Some enter into immune reactions
What does the endoplasmic reticulum do?
Processes molecules made by the cell and transports them to their specific destination in or out of the cell.
What does the golgi apparatus do?
Takes transported substances from the ER to be processed to form lysosomes, secretory vesicles, and other cytoplasmic components
What are lysosomes?
Vesicular organelles that break off from the golgi and provide an intracellular digestive system that allows the cell to digest damaged cellular components, food particles, and unwanted material (bacteria)
What are some common products of hydrolysis?
Protein to AAs
Glycogen to glucose
Lipids to FAs and glycerol
What are the important features of peroxisomes?
Formed by self replication (NOT by the golgi)
Contain oxidases rather than hydrolases
Where are the fibrillar proteins that are used to form the cell's cytoskeleton produced?
Polymers of proteins synthesized by ribosomes in the cytoplasm.
What are the steps of phagocytosis?
1. Cell membrane receptors attach to the surface ligands of the particle
2. Edges evaginate outward to surround the entire particle using contractile actin/myosin to make a closed phagocytic vesicle
3. actin and other contractile fibrils surround the phagocytic vesicle and contract around the outer edge, pushing vesicle to interior
4. Contractile proteins pinch the stem of the vesicle so it separates from the cell membrane to leave the vesicle in the cell interior
What happens after pinocytotic or phagocytotic vesicles are formed?
A digestive vesicle is formed where the hydrolases begin digesting, leading to a residual body that is excreted via exocytosis
What are the bactericidal agents that can kill phagocytized bacteria in lysosomes?
1. Lysozyme: Dissolves bacterial cell membrane
2. Lysoferrin: Binds iron and other substances before they can promote bacterial growth
3. Acid at pH of 5.0 to activate hydrolases and inactivates bacterial metabolic systems
What cellular organelle forms proteins?
Granular (rough) endoplasmic reticulum
What cellular organelle forms lipids
Smooth endoplasmic reticulum
What are the functions of the endoplasmic reticulum?
1. Synth proteins (RER)
2. Synth lipids (SER)
3. Provides enzymes for glycogen breakdown
4. Provides enzymes for detoxifying substances
What are the synthetic functions of the golgi apparatus?
1. Formation of carbohydrates (big polymers like HA and chondroitin)
2. Further processing of substances made in the ER
What is the composition of ATP?
1. Nitrogenous base (adenine)
2. Pentose sugar (ribose)
3. 3 Phosphate radicals
Where does the majority of the cell's ATP formation occur? Through what process?
What are the three major cellular functions of ATP?
1. Transport substances through multiple membranes into a cell
2. Synthesis of chemical compounds throughout the cell
3. Mehanical work
What type of movement is demonstrated by WBC movement through tissues?
How is ameboid movement accomplished?
Protrusion of a pseudopodium occurs from one end of the cell, it attaches to the surrounding tissues, and remainder of cell body is pulled forward to the point of attachment.
What is the most important initiator of ameboid locomotion?
What is the structure of a cilium?
Covered by outcropping of the cell membrane and supported by 11 microtubules. Each cilium is an outgrowth of the basal body of the cilium
What is necessary for continued beating of cilium?
Availability of ATP
Appropriate ionic conditions (particularly magnesium and calcium)
What are some examples of positive feedback mechanisms?
Clotting Cascade, Parturition, Nerve signal transduction
How much of the cell is water?
What are sphingolipids?
Lipids derived from sphingosine that are present in small amounts of cell membranes (particularly nerve cells)
What determines the degree of permeability of the lipid bilayer?
The amount of dissolved cholesterol in the lipid bilayer
What is the function of Hyaluronic Acid/Chondroitin?
1. Major component of proteoglycans
2. Major component of ground substance in the Extracellular matrix
3. Principal component of organic matrix of cartilage/bone
4. Cell activities and migration/proliferation
Sets found in the same folder
Physiology Guyton Ch 6-8
Physiology Guyton Chapter 15
Physiology Guyton Chapter 14
Other sets by this creator
SURGEY 8.1 MIS
PATHO 7.7 LIVER PATHOGY
6.1 GASTROINTESTINAL DRUGS
5.4 VASOACTIVE PEPTIDES