HBY 531 MEDICAL PHYSIOLOGY

Lecture Exam 1

2001

Section 1: Answer the following using:

A = increase

B = not change

C = decrease

1. Following an increase in serum potassium, the volume of most cells will _________.

2. The length constant of an axon will ________ as the membrane capacitance decreases.

3. The force of contraction of a cardiac muscle fiber will ________ after inhibiting the Na⁺/K⁺-ATPase.

4. An increase in the extracellular Mg²⁺ concentration will _________ vesicle fusion at synaptic boutons.

5. An increase in circulating levels of ADH (antidiuretic hormone, or arginine vasopressin) will ________ the membrane hydraulic conductance of the renal collecting duct.

6. The application of furosemide (Lasix^®) to intestinal secretory epithelia will ________ the intracellular Cl^- concentration ([Cl^-]_i).

7. Following local application of caffeine, the duration of norepinephrine release at postganglionic sympathetic motor neuron axon terminals will be expected to ___________________ compared to normal.

8. In the presence of a monoamine oxidase (MAO) inhibitor, the total intracellular dopamine concentration within postganglionic sympathetic nerve terminals will be expected to ____________________.

9. Following infusion of isoproterenol (a non-selective b adrenergic agonist) into the vascular supply of a skeletal muscle, blood flow through that muscle will be expected to _____________________.

10. Following infusion of an M₂ muscarinic agonist into the coronary circulation of the heart, K⁺ conductance will _________________ in heart cells that possess M₂ receptors.

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

11. A cell, initially in equilibrium, contains: concentration of impermeants S_i = 150 mM, and permeants s_i = 150 mM. It is placed in a large bath whose concentration of impermeants S_o = 300 mM, and permeants s_o = 0 mM. Cell volume will:

a. remain constant.

b. double.

c. halve.

d. triple.

e. increase until the cell ruptures.

12. Which of the following is NOT true of osmosis?

a. It is diffusion of water.

b. It moves water from a higher to lower concentration of water.

c. It moves water to even out the concentration of solutes.

d. It moves water from a higher to lower concentration of solutes.

e. It is driven by thermal energy.

13. Which of the following is NOT true of a biomembrane?

a. The lipid phase is impermeable to ions.

b. The lipid phase is impermeable to glucose.

c. The lipid phase is impermeable to small hydrophobic solutes.

d. The proteins mediate transport of ions.

e. The proteins mediate active transport.

14. Which of the following is an example of secondary active transport?

a. Na⁺/Ca²⁺ exchange

b. Na⁺/K⁺ ATPase

c. H⁺ ATPase

d. Electrodiffusion of K⁺

e. Facilitative transport of a solute

15. Membrane capacitance:

a. increases with voltage.

b. increases with charge.

c. depends primarily on membrane proteins.

d. depends primarily on membrane lipids.

e. mediates ion movement across the membrane.

16. A K⁺ channel is determined to have an open channel conductance of 20 x 10^-12 S, and is open on average 5% of the time. If a cell membrane contains 10⁹ of these channels, what is the value of the cells K⁺ conductance due to these channels?

a. 20 x 10^-3 S

b. 50 S

c. 10³ S

d. 10^-3 S

e. 1 mF/cm²

17. Which of the following is NOT true of a Nernst potential?

a. It depends on which membrane channel is open.

b. It is the voltage at which an ion is in equilibrium.

c. It depends on the diffusion gradient for an ion.

d. It can drive ionic current flow when the transmembrane voltage is zero.

e. It does not require charge on the membrane capacitance.

18. If Cl^- is membrane permeant but not actively transported, [Cl^-]_i = 10 mM, and [Cl^-]_o =145 mM, what is this cell’s resting voltage?

a. 60 mV

b. 0 mV

c. -30 mV

d. -70 mV

e. -90 mV

Questions 19 - 21 refer to the figure below

Intracellular Extracellular

[Na]_i = 11mM [Na]_o = 110 mM

[K]_i = 100 mM [K]_o = 1 mM

[Cl]_i = [Cl]_o = 120 mM

[Ca]_i = 450 nM [Ca]_o = 4.5 mM

[A]_i = 120.7 mM

g_K = 1.0 mS/cm²

g_Na = 0.2 mS/cm²

g_Cl = 0.5 mS/cm²

19. What is the value of [Cl]_i?

a. 30.8 mM

b. 10.8 mM

c. 3.8 mM

d. 12.0 mM

e. 1.2 mM

20. What is the resting voltage?

a. 0 mV

b. -30 mV

c. -60 mV

d. -90 mV

e. -120 mV

21. What is the average valence of the impermeant anions, [A]_i ?

a. -1.25

b. -1.00

c. -0.96

d. -0.89

e. -0.75

22. Which of the following is NOT a characteristic of ALL types of action potentials?

a. A voltage and time dependent Na⁺ conductance change

b. An inward current is responsible for depolarization

c. Constant shape within a certain cell type

d. Constant velocity within a certain cell type

e. All or none voltage change

23. Which of the following is a role of action potentials?

a. Regulation of contraction

b. Signal for contraction

c. Transmission of information

d. Signal for exocytosis

e. All of the above

24. During a nerve action potential, the voltage and time dependent increase in K⁺ current:

a. Results from a depolarization in membrane potential.

b. causes the hyperpolarizing afterpotential.

c. is due to an increase in channel open probability.

d. occurs primarily after the large increase in Na⁺-current.

e. All of the above

25. A neuron is voltage clamped to a membrane potential exactly between resting and threshold voltage. After the clamp is released, the net membrane current will be:

a. inward.

b. negative.

c. outward.

d. zero.

e. maximum.

26. During the second half of the relative refractory period,

a. a fraction of activation n-gates of voltage-dependent K⁺-channels are open.

b. a fraction of activation m-gates of voltage-dependent Na⁺-channels are open.

c. there are no Na⁺-channels that have inactivated.

d. a stimulus cannot elicit an action potential.

e. inward currents are larger than during the absolute refractory period.

27. Which of the voltage dependent channels that generate action potential currents has the most rapid activation kinetics?

a. K⁺ channels

b. Ca²⁺ channels

c. Cl^- channels

d. Na⁺ channels

28. At the peak of a nerve action potential, the ratio of sodium to potassium conductance, g_Na:g_K, is 5. If the sodium Nernst potential, E_Na, is +50 mV and the potassium Nernst potential, E_K, is -100 mV, what is the voltage at the peak of the action potential?

a. +100 mV

b. +50 mV

c. +35 mV

d. +25 mV

e. +15 mV

29. Which of the following will decrease the velocity of action potential propagation?

a. A decrease in membrane capacitance

b. An increase in the axon diameter

c. A decrease in axoplasm resistivity

d. An increase in the length constant

e. Loss of the myelin sheath

30. Given below are data for length constant l and capacitance per length C_m of 5 different axons. All else being equal, which has the most rapid action potential propagation velocity?

a. l = 2.0 mm C_m =10 nF/mm

b. l = 1.5 mm C_m =10 nF/mm

c. l = 2.0 mm C_m =15 nF/mm

d. l = 1.5 mm C_m =15 nF/mm

e. l = 2.5 mm C_m = 5 nF/mm

31. Which of the following is NOT true of a chemical synapse?

a. Neurotransmitter is synthesized in the presynaptic cell body.

b. There is a gap between the pre- and postsynaptic cells.

c. Presynaptic transmitter release involves presynaptic Ca²⁺ entry.

d. The postsynaptic response involves binding of transmitter to a postsynaptic receptor.

e. Termination of the postsynaptic response involves reduction of transmitter concentration in the synaptic gap.

32. Eserine inhibits the ACh esterase. At the neuromuscular junction, eserine would be expected to:

a. decrease MEPP amplitude.

b. decrease MEPP frequency.

c. increase MEPP frequency.

d. increase MEPP duration.

e. decrease MEPP duration.

33. Which of the following is a property of the ACh receptor?

a. It is an anion channel.

b. It gates open after binding of one Ach molecule.

c. It catalyzes the breakdown of ACh.

d. It resides in the presynaptic terminal.

e. It allows monovalent cations to cross the postsynaptic membrane.

34. In the CNS, spatial summation refers to:

a. an excitatory postsynaptic response.

b. an inhibitory postsynaptic response.

c. the postsynaptic response to a rapid series of presynaptic action potentials at one presynaptic terminal.

d. the postsynaptic response to several presynaptic action potentials arriving nearly simultaneously at different presynaptic terminals.

e. the simultaneous response in several different postsynaptic cell bodies.

35. A postsynaptic receptor activates a G protein that decreases the open probability of Ca²⁺ channels and increases the open probability of K⁺ channels.

a. This is a fast, excitatory synapse.

b. This is a slow, excitatory synapse.

c. This is a slow, inhibitory synapse.

d. This is a fast, inhibitory synapse.

e. This synapse is both inhibitory and excitatory.

36. The transmitter at a synapse activates a postsynaptic channel that is equally selective for mono valent cations. If the postsynaptic cell body had an initial voltage of -70 mV, E_Na = + 70 mV, E_K = -100mV, and E_Cl = -70 mV, the new postsynaptic voltage will be:

a. 0 mV.

b. Between -70 mV and -100 mV.

c. Between -70 mV and 0 mV.

d. -70 mV.

e. Negative to -100 mV.

Questions 37 and 38 refer to the sketch of thick and thin filaments below.

37. The sarcomere lengths where maximum active forces are generated are:

a. greater than 2.5 mm.

b. between 1.7 mm and 2.5 mm.

c. between 1.5 mm and 1.7 mm.

d. between 1.0 mm and 1.5 mm.

38. The sarcomere lengths where there is no active force generated are:

a. greater than 2.5 mm.

b. between 1.7 mm and 2.5 mm.

c. between 1.5 mm and 1.7 mm.

d. between 1.0 mm and 1.5 mm.

39. In cardiac and skeletal muscle, cross bridge binding to actin sites is inhibited by:

a. [Ca²⁺]_i.

b. troponin/tropomyosin.

c. the myosin kinase.

d. ATP.

e. creatine phosphate.

40. In which type of muscle does a single action potential NOT directly regulate force of contraction?

a. Smooth muscle

b. Cardiac muscle

c. Skeletal muscle

41. A muscle of unknown origin appears striated. When it is placed in a solution containing no Ca²⁺, it will not contract when stimulated. This cell is from:

a. smooth muscle.

b. cardiac muscle.

c. skeletal muscle.

42. In which type of muscle is total force NOT regulated through temporal summation?

a. Smooth muscle

b. Cardiac muscle

c. Skeletal muscle

43. Which membrane system conducts the action potential radially into a skeletal muscle cell?

a. The terminal cisternae

b. The surface membrane

c. The sarcoplasmic reticulum

d. The mitochondria

e. The T system

44. Which of the following combinations of types of muscle would be the least likely to occur?

a. Type I, aerobic

b. Type I, glycolytic

c. Type IIx, glycolytic

d. Type IIa, glycolytic

e. Type IIa, aerobic

45. Two skeletal muscle cells are isolated. Both are Type I but cell 1 is twice the length and twice the diameter of cell 2. Which of the following is correct?

a. Cell 1 contracts twice as fast and four times more strongly than cell 2.

b. Cell 1 contracts twice as fast and two times more strongly than cell 2.

c. Cell 1 contracts four times as fast and two times more strongly than cell 2.

d. Cell 1 contracts half as fast and four times less strongly than cell 2.

e. Cell 1 contracts half as fast and half as strongly as cell 2.

46. Regarding the tight junctions of epithelial cells, which of the following statements is FALSE?

a. They permit the passage of small intracellular solutes between neighboring epithelial cells.

b. They aid in fastening (holding) adjacent cells together.

c. They prevent lateral diffusion of membrane lipids and proteins between the apical and basolateral membranes.

d. They mediate the selectivity barrier for paracellular transepithelial transport especially important in tight epithelia.

47. A square centimeter of an epithelium is absorbing Na⁺ at a sustained rate of 30 mA (i.e., there is an apical Na⁺ current of -30 mA). The epithelium adheres to the Ussing model for Na⁺ absorption. Assuming that the epithelium is in a steady-state (i.e., cell volumes and intracellular concentrations are not changing), what is the NET current being carried by the sodium pump (Na⁺,K⁺-ATPase)? (Hint: Recall that the pump pumps out 3 Na⁺ ions in exchange for pumping in 2 K⁺ ions.)

a. A net outward pump current of 30 mA/cm².

b. A net inward pump current of 20 mA/cm².

c. A net outward pump current of 10 mA/cm².

d. Zero net current is being carried by the sodium pump.

48. Regarding RBC production (erythropoiesis), which of the following statements is FALSE?

a. Pernicious anemia results from a lack of vitamin B₁₂ (cyanocobalamin) and can be caused by lack of intrinsic factor, a substance secreted by acid-producing cells of the stomach.

b. Erythropoiesis is stimulated by erythropoietin, a hormone secreted by the kidney that stimulates the proliferation of cells in the bone marrow.

c. On a daily basis, one must absorb, from the gastrointestinal tract, sufficient iron for the synthesis of hemoglobin since iron derived from RBC breakdown is excreted with bilirubin into the bile.

d. On average, the body makes about 30 gm of RBCs per day, an amount that balances the daily removal of old RBCs by macrophages in the spleen and the reticuloendothelial system.

49. Which of the following would NOT be expected to cause jaundice?

a. Gallbladder disease causing blockage of the bile duct.

b. Severe liver disease like hepatitis.

c. Pernicious anemia caused by the inability to absorb vitamin B₁₂.

d. Hemolytic anemia caused by abnormally high rates of RBC breakdown by macrophages.

50. Iron in the plasma is asso