HBY 531 MEDICAL PHYSIOLOGY

Lecture Exam 1

2002

Section 1: Answer the following using:

A = increase

B = not change

C = decrease

1. A toxin inserts into the cell membrane where it forms a non-selective ion channel. The ion permeability of the membrane is significantly increased. As a result, cell volume will _______A________.

2. A cardiac myocyte is exposed to ouabain at a physiologically effective concentration. As a result, cell Ca²⁺ concentration will ______ A________.

3. A hydrophobic chemical inserts into a cell’s membrane and causes the membrane capacitance to increase from 1 FF/cm² to 2 FF/cm². All else remaining equal, the membrane voltage will ______ B________.

4. In a cell at rest, Cl^- is in equilibrium. A hormone binds and causes an increase in chloride conductance, g_Cl. The chloride current, i_Cl, will _______B________.

5. A nerve axon is isolated and its action potential recorded. The voltage dependent potassium conductance is blocked with TEA. The presence of TEA will cause action potential duration to _______ A________.

6. When a nerve cell membrane is slowly depolarized form -70 mV to -20 mV, the Na⁺-channel inactivation gate open probability, h, will _______C________.

7. Demylination of axons causes action potential propagation velocity to ______C_________.

8. At the neuromuscular junction, the presence of an acetylcholine esterase inhibitor will cause the duration of miniature end plate potentials to _______ A________.

9. At a synapse in the CNS, an increase in presynaptic action potential frequency causes an increase in inward current in the postsynaptic cell. As a result, postsynaptic action potential frequency will ______ A_________.

10. In cardiac muscle, a small increase in the preload will _______ A________ force generation.

11. In skeletal muscle, an increase in external Ca²⁺-concentration will _______B_______ twitch amplitude.

12. Weight training will ______B_________the number of muscle cells.

13. When complex carbohydrates (e.g., starch) are present in the small intestinal lumen, pancreatic amylase is released that dramatically increases the rate of digestion (hydrolysis) of the carbohydrates. This will _____A____ the flow of water into the intestinal lumen.

14. An decrease in the luminal concentration of glucose in the small intestines will _____C____ the inward sodium current into absorptive mucosal epithelial cells.

15. Low plasma O₂ concentration is sensed by the kidney, and as a result the kidney releases a hormone. The hormone will _____B____ the number of pluripotent stem cells in the marrow.

16. Release of norepinephrine from presynaptic adrenergic nerve terminals will ___A____ following application of an a₂ antagonist.

Section 2: For each of the following, choose the single best response.

17. A cell, initially in equilibrium, contains: concentration of impermeants S_i = 200 mM, concentration of permeants s_i = 100 mM. It is placed in a large bath containing: concentration of impermeants S_o = 200 mM, concentration of permeants s₀ = 150 mM. The ratio of final volume to initial volume is:

a. 1:1.

b. 2:3.

c. 3:2.

d. 2:1.

e. 1:2.

18. A solution contains (in mM): NaCl 50; CaCl₂ 100; sucrose 100. Assuming osmotic coefficients are approximately unity, the solution osmolarity is approximately:

a. 200 mOsm.

b. 250 mOsm.

c. 300 mOsm.

d. 400 mOsm.

e. 500 mOsm.

19. The transporter responsible for maintaining the transmembrane gradients that are used to set the cell’s resting voltage is called the:

a. Na⁺/Ca²⁺ exchanger.

b. Ca²⁺ ATPase.

c. H⁺ ATPase

d. Na⁺/K⁺ ATPase

e. Na⁺-K⁺-2Cl^- cotransporter.

20. Which of the following pathways is not used for ion transport into and out of cells?

a. Endocytosis and exocytosis

b. The lipid bilayer

c. Channel forming proteins

d. Primary active transport

e. Secondary active transport

21. The conductance of a biomembrane is due to:

a. the lipid bilayer.

b. the dielectric constant of oil.

c. integral membrane proteins.

d. the surface charge.

e. the membrane voltage.

Questions 22-24 refer to the figure below showing a cell in an infinite bath.

[Na⁺]_o = 144 mM

[K⁺]_o = 4 mM

[Ca²⁺]_o = ?

[Cl^-]_o = 152 mM

g_K = g_Cl = 1.1x10^-3 S/cm²

g_Na = 0.025x10^-3 S/cm²

Assume that: 1) The cell is oin steady-state; 2) the average valence of the impermeant anions is not known; 3) Na⁺, Ca²⁺ and K⁺ are actively transported, but Cl^- is not.

22. [Ca²⁺]_o =

a. 1 mM

b. 2 mM

c. 3 mM

d. 4 mM

e. 5 mM

23. R_i =

a. +69.5 mV

b. -92.5 mV

c. -89 mV

d. -60 mV

e. +60 mV

24. [A]_i =

a. 147 mM

b. 149 mM

c. 151 mM

d. 153 mM

e. 155 mM

25. The peak of a nerve action potential is +50 mV. If E_Na = +60 mV and E_K = -100 mV, what is the ratio of g_Na/g_K at the peak of the action potential?

a. 1

b. 5

c. 10

d. 15

e. 20

26. A nerve action potential is recorded: (1) in control conditions; and (2) after block of the voltage and time dependent g_K. In record (2) relative to control record (1) the:

a. action potential duration is shorter.

b. action potential duration is longer.

c. action potential height is less.

d. hyperpolarizing after potential is more negative.

e. two records are the same.

27. During the relative refractory period,

a. g_Na is elevated over rest.

b. threshold is more positive than at rest.

c. inward current exceeds outward current.

d. g_K is inactivated.

e. none of the above is true.

28. Na⁺-channels have activation (m) and inactivation (h) gates. K⁺-channels have activation (n) gates. T-type Ca²⁺-channels have activation (a) and inactivation (i) gates. Which gates respond most rapidly to changes in membrane voltage?

a. (i)

b. (a)

c. (n)

d. (h)

e. (m)

29. Which of the following does not affect action potential propagation velocity?

a. Membrane capacitance

b. Axon diameter

c. Length constant

d. Peak g_Na

e. Peak g_K

30. Which of the following does not contribute to, or result from, the process of myelination?

a. Nodes of Ranvier

b. Increased propagation velocity

c. Schwan cells

d. Calcium currents

e. Decreased axon capacitance

31. At the neuromuscular junction, acetylcholine (ACh) binds to a channel that is selective for which ion(s)?

a. Na⁺

b. Ca²⁺

c. K⁺

d. Monovalent cations.

e. Monovalent anions.

32. Myasthenia gravis has caused a person to lose a large fraction of their ACh receptors. The miniature end plate potentials (MEPPs) recorded in muscles from this person will be:

a. longer in duration than normal.

b. more frequent than normal.

c. larger in amplitude than normal.

d. smaller in amplitude than normal.

e. the same as normal.

Questions 32 and 33 refer to the two figures and data shown below.

Assume we are using the whole cell patch technique to record either the postsynaptic potential (R_ps) or the postsynaptic current (I_ps) from the cell body of an "-motor neuron. The following data are determined when the axon is not stimulated.

R_ps = -76 mV

g_m = g_K +g_Na + g_Cl = 0.21 mS/cm²

g_K = 0.10 mS/cm² E_K = -90 mV

g_Cl = 0.10 mS/cm² E_Cl = -76 mV

g_Na = 0.01 mS/cm² E_Na = +60 mV

g_Ca = 0 E_Ca = +100 mV

The following data were obtained by voltage clamping the post synaptic potential (R_ps) to the values indicated on the right-hand side of the graph while stimulating pre-synaptic action potentials (APs) with STIM at the arrows below the graph. The curves indicate just the change, )i_X, in current elicited by a stream of APs from the STIM.

33. The transmitter released by the STIM increases the postsynaptic conductance of which ion(s)?

a. Na⁺

b. Ca²⁺

c. K⁺

d. Cl^-

e. Cations

34. If the postsynaptic cell body were not voltage clamped, what would the value of R_PS be due to activation of )g_X?

a. -86 mV

b. -76 mV

c. -49 mV

d. -30 mV

e. -10 mV

35. In smooth muscle, cross bridge binding to actin is inhibited by:

a. [Ca²⁺]_i.

b. troponin.

c. tropomyosin.

d. a myosin phosphatase.

e. a myosin kinase.

36. The sliding filament theory of muscle contraction applies to:

a. cardiac muscle only.

b. cardiac and skeletal muscle.

c. cardiac, skeletal and smooth muscle.

d. skeletal muscle only.

e. smooth muscle only.

37. In skeletal muscle, the site of release of the Ca²⁺ that regulates contraction is:

a. the T-system.

b. the plasma membrane.

c. the longitudinal S. R.

d. the terminal cisternae.

e. the mitochondria.

38. You are given 3 strips of muscle of unknown origin. When placed in a Ca²⁺-free external solution, muscle 1 and muscle 2 will not contract when stimulated, but muscle 3 will contract. In normal external solution, when the three muscles are subjected to a prolonged rapid series of stimulations by external electrodes, muscle 2 and muscle 3 go into a prolonged contraction whereas muscle 1 contracts then relaxes at a rate much lower than that of the series of shocks. You conclude that:

a. Muscle 1 = skeletal; Muscle 2 = cardiac; Muscle 3 = smooth

b. Muscle 1 = cardiac; Muscle 2 = smooth; Muscle 3 = skeletal

c. Muscle 1 = smooth; Muscle 2 = skeletal; Muscle 3 = cardiac

d. Muscle 1 = smooth; Muscle 2 = cardiac; Muscle 3 = skeletal

e. Muscle 1 = cardiac; Muscle 2 = skeletal; Muscle 3 = smooth

39. You are given 2 cardiac muscle cells that have the same length, but cell 2 is twice the diameter of cell 1. The ratio of force production by cell 2 to cell 1 is:

a. 1:1.

b. 2:1.

c. 3:1.

d. 4:1.

e. 8:1.

40. In a skeletal muscle containing a mix of type I slow twitch and type II fast twitch motor units, which of the following statements is true concerning unit size and recruitment?

a. Type II are small and are recruited first; Type I are large and are recruited last

b. Type II are large and are recruited first; Type I are small and are recruited last

c. Type I are large and are recruited first; Type II are small and are recruited last

d. Type I are small and are recruited first; Type II are large and are recruited last

e. Type I are small, type II are large; but there is no consistent pattern.

41. Regarding the function of epithelial tight junctions, which of the following statements is FALSE?

a. They aid in preventing the migration of apical membrane proteins to the basolateral membrane.

b. They aid in preventing the migration of basolateral membrane proteins to the apical membrane.

c. They exhibit specific permeability properties that regulate the paracellular transepithelial transport of solutes.

d. They form channels that facilitate the movement of small intracellular solutes between neighboring cells.

e. They aid in physically attaching neighboring cells to one another.

42. Which of the following would most likely be classified as a tight epithelium (e.g., an epithelium possessing tight junctions with low transepithelial permeability)?

a. Gastric (stomach) mucosa

b. Absorptive epithelial cells of the small intestine

c. Proximal tubule of the nephron

d. Secretory epithelial cells of the small intestine

e. Gallbladder epithelium

43. When bathed by identical Ringer’s solutions on both sides, an epithelium is found to have a transepithelial potential of -80 mV and a basolateral membrane potential of -60 mV (both potentials measured with respect to the serosa). Equilibrium potentials are as follows: E_Na is +50 mV, E_K is -100 mV and E_Cl is -60 mV. Under these conditions, which of the following statements is FALSE? E was also false and credit was given for both. (if absorption was changed to secretion e would have been true)

a. The apical membrane potential is -20 mV (measured with respect to the mucosa).

b. An apical membrane sodium conductance (g_Na) would result in passive sodium absorption into the cells.

c. An apical membrane chloride conductance (g_Cl) would result in passive chloride absorption into the cells.

d. A basolateral membrane potassium conductance (g_K) would result in an outward potassium current.

e. If the tight junctions were cation permeable, one would observe transepithelial absorption of both sodium and potassium.

44. Regarding the secretion of gastric (stomach) acid by parietal (oxyntic) cells, which of the following statements is FALSE?

a. The ultimate source of H⁺ is carbonic acid (H₂CO₃) derived from the reaction of CO₂ and water.

b. Acid secretion involves the activity of a mucosal ATPase that secretes H⁺ in exchange for the absorption of potassium.

c. Acid secretion rate is increased by increasing the apical-membrane conductance to H⁺.

d. Actively secreting cells exhibit highly invaginated apical canaliculi.

e. Acid secretion involves the concomitant production of bicarbonate, which exits the basolateral membrane via a chloride-bicarbonate exchanger.

45. Regarding the cellular components of blood, which of the following are classified as cell fragments derived from megakaryocytes?

a. Erythrocytes

b. Leukocytes

c. Granulocytes

d. Lymphocytes

e. Thrombocytes

46. Low plasma levels of which of the following proteins is diagnostic of anemia caused by iron deficiency? B was accepted, even though c is diagnostically correct.

a. Hemoglobin

b. Transferrin

c. Ferritin

d. Myoglobin

e. Fibrinogen

47. Thoracic splanchnic nerves contain axons of:

a. preganglionic sympathetic motor neurons.

b. postganglionic sympathetic motor neurons.

c. preganglionic parasympathetic motor neurons.

d. visceral afferent neurons.

e. both a and d.

48. With regard to bladder function, infusion of atropine (a non-specific muscarinic antagonist) to the bladder would inhibit contraction of:

a. the external urethral sphincter .

b. the internal urethral sphincter.

c. the smooth muscle of the trigone.

d. the detrusor muscle.

e. all of the above.

49. Reserpine was used historically to treat hypertension, an effect presumably based on it’s ability to block:

a. choline uptake into presynaptic nerve terminals.

b. acetylcholine release at cholinergic synapses.

c. norepinephrine uptake into synaptic vesicles.

d. acetylcholine uptake into synaptic vesicles.

e. feedback inhibition of norepinephrine release mediated by stimulation of presynaptic adenosine receptors.

50. A patient accidentally exposed to an acetylcholine esterase inhibitor would benefit from which of the following?

a. Atropine

b. Nicotine

c. A Ca²⁺ ionophore

d. A monoamine oxidase (MAO) inhibitor

e. Reserpine