Physiology - Cellular Physiology
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67 terms
Terms | Definitions |
|---|---|
 Explain the concept of homeostasis | the maintenance of steady state within the body environment - takes energy - maintain internal stability owing to the coordinated response of its parts to any situation or stimulus that disturbs it's normal condition or function |
| Discuss the relationship between the external and internal environments | variable temp outside -> 37C inside, high O2 outside -> low O2 inside, low CO2 outside -> high CO2 inside, variable pH outside -> 7.4 inside |
| List the components of and the relationship between the 3 major body fluid compartments | 3L of blood plasma (high Na/Cl, low K), 28L of intracellular (low Na/Cl, high K, high proteins), 11L of interstitial (high Na/Cl, low K, no proteins), 1L of transcellular (CSF and joints). All have osmolality of 290 mOsm |
| Give examples of processes controlled by homeostatic mechanisms in the body | blood pressure regulation, glucose/insulin feedback, |
| Explain the concept of negative feedback | change is sensed and and action is taken to prevent further change. When there is change in a controlled variable, there is a sensor which sends the information to a comparator, which causes an effector to bring the controlled variable back to the set point. These processes can be in separate locations (BP regulation) or all in the same cell (b-cells in blood glucose regulation) |
| Define controlled variable | some variable that is controlled by homeostasis mechanisms (BP, glucose levels, pH) |
| Define sensor | takes in sensory information and sends it to the comparator - e.g. barroreceptors in the carotid sinus or aortic arch |
| Define comparator | usually the brain - knows set point and takes info from sensor and uses effector to get back to set point of a controlled variable |
| Define set point | the set level for a controlled variable |
| Discuss factors that may produce a deviation in set points | can vary from person to person or over time with same individual. Deviations can be protective (K secretion is slower through the night) or pathological (chronic increase in BP). Circadian rhythm allows for set points to vary between active and passive times. |
| Explain the concept of positive feedback | change is sensed and action is taken to amplify a change (usually associated with a discrete end point) i.e. birth, ovulation, orgasm, blood clotting |
| Explain the concept of feed-forward regulation | anticipation of change - heart rate and ventilation increase before exercise, salivation and digestive enzyme production before a meal |
| Define and explain redundancy and hierarchy with respect to homeostatic control systems | important mechanisms usually have more than 1 control mechanisms (backup system) - e.g. blood pressure, control of blood vessels, airway surface liquid secretion. There is a hierarchy of responses (ex. skin blood vessel diameter during exercise) |
| Is heart rate a homeostatically controlled variable? | No, there is no sensor for HR and no set point |
| Pavlov's dog's salivation when hearing the bell ring is an example of | feed forward regulation |
| Define equilibrium | no net flux of energy from one compartment to the other, forward reaction = reverse reaction |
| Define steady state | parameters do not change over time - requires energy |
| Osmolality | number of osmotically active particles per kg of water |
| Osmolarity | number of osmotically active particles per L of water |
| Discuss and explain passive diffusion across an ideal semi-permeable membrane | random thermal motion due to molecular kinetic energy |
| Describe the change in solute concentrations between solute compartments due to passive diffusion | results in equal distribution in both compartments over a period of time |
| List and explain the factors that influence net flux across a membrane | the permeability of that membrane (the partition coefficient, the diffusion coefficient and the thickness), the area, the concentration gradient |
| Calculate net flux of a solute across an ideal semi-permeable membrane | Flux (J) = Permeability (P) x Area (A) x Concentration gradient [(X]0-[X]i) |
| Describe the mechanism of action and the effect of ion channels on net flux | once either ligand is bound or certain voltage is reached, a transmembrane protein opens its pore and increases the net flux by decreasing membrane permeability |
| List and explain factors that regulate ion channels | can be ionotropic (ligand binds and channel opens), metabotropic (activates second messenger which activates a remote set of channels) or voltage gated (charged amino acids detect electric field and cause conformational change) or mechanosensitive (stretching) - all require a concentration gradient |
| Explain channel specificity | depends on charge of amino acids and size of the pore (K is bigger than Na) |
| Discuss membrane pores | open transmembrane proteins - mostly in the nucleus, happens in apoptosis - increases membrane permeability |
| Discuss and explain mediated transport | solute binds to a specific site on the membrane protein - conformational change - site is now exposed to other side of the membrane - solute is free to leave the protein |
| List and explain the major factors determining the rate of transport in mediated transport | Saturation of transporters (how many binding sites), number of transporters, time for transport to physically change, and the electrochemical gradient of the solute across the membrane |
| Describe the mechanism of facilitated diffusion | electrochemical gradient provides driving force - transporters are specific for substrate, have a maximum transport rate (saturation kinetics). More transporters = more flux. |
| Discuss net flux vs. concentration gradient in facilitated diffusion | increases and eventually hyperbolically decreases the rate due to the saturation kinetics which causes a maximum transport rate depending on the rate at which the transporter can open and close |
| Discuss and explain active transport | uses ATP - move ions against the electrochemical gradient for that ion (can generate a voltage difference across the membrane) |
| Compare and contrast primary and secondary active transport | primary requires direct expenditure of energy and secondary couples with another ion concentration gradient to move the solute against its gradient |
| Discuss co-transporters | Na/glucose co-transporter uses sodium to bring in a glucose with it |
| Discuss exchangers | Na/Ca exchanger uses the Na ion gradient to move an Na ion inside the cell and move a Ca out (calcium ions are toxic to the cell |
| Describe and explain endocytosis and exocytosis | Endocytosis = engulf part of extracellular fluid, pinch off and release contents into the cell. Exocytosis = vesicle fuses with plasma membrane to release contents to extracellular fluid |
| Describe and explain epithelial transport | SECRETION: sodium is pumped in via a triple co-transporter with chloride ions, CFTR sends Cl to apical surface -> electrochemical gradient drives Na+ to the apical surface - water follows salt. Absorption - Na is absorbed by eNaC, Na is pumped out of the cell through the basal surface - Cl follows and water is absorbed |
| Calculated and explain the concepts underlying partial pressures of gases | total barometric pressure is the sum of the partial pressures of each of the individual gases |
| Discuss and explain the movement of gases between air and liquid | gases always flow down a partial pressure gradient, the amount of gas that will dissolve Henry's law: dissolved gas = solubility coefficient x partial pressure of a gas |
| Discuss and explain water movement across membranes | water will move down its concentration gradient (Na will suck water towards it) - water can diffuse across lipid bilayers |
| Describe the role of aquaporins in water movement across membranes | proteins that act as water channels in the plasma membrane and help increase flux (depends on osmotic gradients) |
| Discuss and explain the forces driving water movement across membranes | osmotic and hydrostatic forces |
| Define and explain osmotic force | water moves toward area of high solute concentration (low water concentration) - depends on reflection coefficient of membrane for a given solute |
| Define and explain hydrostatic force | the effect of gravity on the fluid (plus hydraulic pressure if fluid is moving) |
| Calculate the net flux of water across a membrane | Water flux = water permeability (Lp) x [Osmotic gradient + pressure gradient] |
| Calculate the osmotic pressure gradient | Osmotic pressure gradient = RT x (difference in osmolality between 2 compartments: outside - inside) |
| Iso-osmotic | same solute concentration - happens often when membrane is fully permeable to solute |
| Define and explain osmolality and tonicity | Osmolality = comparing number of osmotically active particles. Tonicity = comparing number of osmotically active NON-PENETRATING particles |
| Discuss the effect of hypertonic, isotonic and hypotonic solutions on cell volume | hypertonic means that there is more non-penetrating particles in the ECF (water flows out - cell shrinks), isotonic means that there is equal non-penetrating particles in the ECF and ICF (cell size does not change), hypotonic means there are less non-penetrating particles in the ECF than the ICF (water flows into the cell - swells) |
| What type of solution would you give a person with dehydration | use a hypotonic solution - want cells to fill up with water - use 1/2 saline (hypo-osmotic/hypotonic) or 5% dextrose with 1/2 saline (hyperosmotic/hypotonic) |
| What type of solution would you give a person with blood (volume) loss | use an isotonic solution - don't want cell to swell or shrink - either pure .9% saline (iso-osmotic/isotonic) or 5% dextrose with .9% saline (dextrose is a penetrating particle so there is equal non-penetrating particles in the ECF and ICF - hyperosmotic/isotonic) |
| Discuss paracellular and transcellular water movement | water can go through the cell (transcellular) or through the tight junctions between the cells (paracellular) |
| Discuss and explain the resting membrane potential | set by ionic gradients and the channels present in the membrane. -50mv for epithelial and -80mv for a neuron (excitable) |
| Describe the buildup of negative and positive charges on either side of the cell membrane | opposite charges are attracted to each other at the membrane, overall the net charge within the cell and within the ECM is still 0 |
| Compare and contrast the different forces acting on ions at resting membrane potential and at the ions equilibrium potential | concentration and electrical gradients equilibrate where there is no net flow of ions (electrochemical gradient) is 0; there is still a concentration gradient though! |
| Discuss the role of the Na+/K+ pump in the maintenance of the resting membrane potential | Has very little to do with the negative membrane potential - mostly K+ channels |
| Calculate equilibrium potentials for various ions | for positive ions E=-60 log (ions inside/ions outside), negative ions is (ions outside/ions inside). |
| Calculate the membrane potential using the Nernst equation | Membrane potential = sum of E for each ion channel/ total # of ion channels |
| Calculate the electrochemical gradient | Electrochemical gradient = membrane potential - equilibrium potential for an ion (+ value means ion will move out of cell) |
| Discuss graded potentials, compare and contrast depolarization and hyperpolarization | graded effect = larger stimulus, larger depolarization. Depolarization is going back towards 0 (making it less negative); hyperpolarization is going away from O (more negative) |
| Explain the permeability coefficient | 1 = non-permeable, 0 = permeable |
| Explain driving force | DF = Vm - Em = difference between recorded difference and equilibrium potential |
| Describe and explain the physiological mechanisms underlying the action potential | 1 - Sodium moves into cell interior to get depolarization 2 - Hits a threshold point which triggers more sodium channels to open and Vm approaches E (Na) 3 - Na channels begin to switch off while K+ channels open to get hyperpolarization 4 - Na channels close and Vm approaches E (K+) |
| Explain the properties of voltage gated Na channels | in rest: activation gate closed, inactivation gate open (no Na flux). In Depolarization phase: activation gate opens (full Na flux). Repolarization phase: activation gate open but inactivation gate closed (no flux, channel can't be activated). Channel then resets to resting |
| Define absolute refractory period | during repolarization, channel can't be activated because inactivation gate is closed. Cannot be reactivated until activation gate closes and inactivation gate opens again |
| Define relative refractory period | Only a stronger than normal stimulus can evoke an action potential (inhibited but not impossible) |
| Why is a cell interior negative? | K+ channels are leaky - K+ is most permeable and therefore Vm is close to E (K+) |
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