Biology 449 - Animal Physiology

Fall 2005

Midterm 2 - Key

Fill in your scantron form as follows. This is worth 1½ points:

· Write and bubble in your name in the upper left (last name first).

· Follow any additional instructions provided in class.

· Sign your form in the upper right.

Multiple choice: As always, choose the best answer for each multiple-choice question. Answer on your scantron form. Each question is worth 1½ points.

1. Chodrocytes are cells that

a. lay down bone.

b. break down bone.

c. lay down cartilage.

d. break down cartilage.

e. release IGF-I.

2. Growth hormone levels increase to at least some degree

a. shortly after going to sleep.

b. shortly after eating.

c. when exercising.

d. a and b.

e. a and c.

3. After reaching adulthood, growth in height in humans can be renewed by

a. injecting increased amounts of growth hormone.

b. injecting increased amounts of sex hormones.

c. injecting increased amounts of growth and sex hormones.

d. injecting IGF-I.

e. Additional growth in height in adults is not possible.

4. The thin filaments of a sarcomere are anchored on the

a. foot proteins.

b. globular actin.

c. myosin tails.

d. sarcoplasmic reticulum.

e. Z-line.

5. If a muscle fiber were injected with a substance that poisoned the transporters that move calcium back into the sarcoplasmic reticulum, the likely result of a single action potential in the fiber would be

a. no force production be the fiber.

b. a longer than normal latent period.

c. much slower force development than normal.

d. much lower force production than normal.

e. much longer force production than normal.

6. The myosin binding sites on actin are exposed from beneath tropomyosin when

a. actin undergoes a conformation change.

b. dihydropyridine undergoes a conformation change.

c. myosin undergoes a conformation change.

d. tropomyosin undergoes a conformation change.

e. troponin undergoes a conformation change.

7. The force produced by a muscle is being measured as it contracts under isometric conditions. If the muscle is held at a length of 6 cm during contraction, it produces 10 N of force, but only produces 5 N when held at a length of 8 cm. Which of the following best explains this observation?

a. The weight the muscle is lifting has increased.

b. The weight the muscle is lifting has decreased.

c. Thick filaments are being compressed against the ends of the sarcomere.

d. There is less overlap between thick and thin filaments.

e. None of the above could explain these observations.

8. A twitch contraction is best defined as

a. a contraction triggered by a single action potential.

b. a contraction involving only one motor group.

c. contraction by a fast glycolytic or oxidative fiber.

d. a contraction in which the muscle shortens by only a small amount.

e. a contraction with a short latent period.

9. In mammals, which of the following can be changed by different patterns of physical activty?

a. The number of fibers in a muscle.

b. The type of myosin ATPase in a fiber.

c. The oxidative capacity of a fiber.

d. Two of the above.

e. All of the above.

10. Which of the following best describes how the activity of a whole muscle is controlled to produce an appropriate level of force production for a particular task?

a. Fibers are individually innervated and activated to generate the required amount of force.

b. Fibers are activated innervated and activated in groups to generate the required amount of force.

c. All the fibers in a muscle are activated with action potentials of a magnitude suitable to generate the required amount of force.

d. All the fibers in a muscle are activated with action potentials at a frequency suitable to generate the required amount of force.

e. All the fibers in a muscle are activated with the sarcomeres at an appropriate length to generate the required amount of force.

11. Which type of blood vessel has highly elastic walls?

a. Arteries

b. Capillaries

c. Veins

d. a and c are about equal in elasticity.

e. a, b and c are about equal in elasticity.

12. The heart muscle gets its oxygen

a. by direct diffusion from the adjacent lungs.

b. from the blood that passes through the atria and ventricles.

c. from the blood [that] passes through the coronary arteries and then to capillaries in the heart.

d. from myoglobin stores.

e. The heart does not need oxygen since it relies on anaerobic metabolism.

13. Which of the following statements about ventricular filling is not true?

a. The ventricles will fill when blood pressure in the atria exceeds pressure in the ventricles.

b. Blood enters the ventricles only when the atria contract.

c. The semilunar valves prevent blood from the arteries from reentering the ventricles.

d. The volume of blood that enters the ventricles during ventricular diastole is variable.

e. Ventricular filling stops at the beginning of ventricular systole.

14. If total peripheral resistance drops, which of the following changes would be expected as the regulatory response?

a. an increase in blood pressure.

b. a decrease in blood pressure.

c. an increase in cardiac output.

d. a decrease in cardiac output.

e. Two of the above.

15. According to Poiseuille’s Law, the flow of fluid through a tube changes in direct proportion to

a. the radius of the tube.

b. the length of the tube.

c. the viscosity of the fluid.

d. the pressure differential along the tube.

e. Two of the above.

Flow changes in direct proportion to the radius⁴, not the radius, but this distinction was apparently unclear to many people. I will likely give credit for either d or e.

16. Ions and glucose generally make their way from the blood in a capillary to adjacent tissues

a. by diffusing through the membranes of the endothelial cells.

b. by passing though pores between the endothelial cells.

c. by transport across the endothelial cells using carrier proteins.

d. by transport across the endothelial cells in vesicles.

e. Ions and glucose do not exit the blood in capillaries.

17. The elasticity of the lungs is due to

a. the presence of elastin fibers.

b. the surface tension of the fluid lining the alveoli.

c. the compressive force of the intrapleural membrane.

d. Two of the above. (a and b)

e. All of the above.

18. Atmospheric pressure at 2000 meters is about 600 torr. Given this, what is the approximate partial pressure of oxygen at this altitude?

a. < 1 torr

b. 104 torr

c. 126 torr

d. 160 torr

e. 600 torr

19. During inhalation, the movement of air into the lungs results from

a. diffusion driven by low partial pressure of oxygen in the alveoli

b. diffusion driven by high partial pressure o carbon dioxide in the alveoli.

c. bulk flow driven by lowered hydrostatic pressure in the alveoli.

d. bulk flow driven by increased hydrostatic pressure in the pharynx.

e. Two of the above.

20. If a person at rest consciously forced her tidal volume (the volume of air per breath) to increase from 500 to 1000 ml without doing anything else differently

a. her alveolar ventilation rate would double and alveolar P_CO2 would decrease.

b. her alveolar ventilation rate would more than double and alveolar P_CO2 would decrease.

c. her alveolar ventilation rate would double and alveolar P_CO2 would increase.

d. her alveolar ventilation rate would more than double and alveolar P_CO2 would increase.

e. None of the above would be true.

21. In order to determine whether a dissolved gas will diffuse from fluid A to fluid B or from B to A, you need to know

a. the partial pressures of the gas in A and B.

b. the concentrations of the gas in A and B.

c. the solubility of the gas in A and B.

d. Two of the above.

e. All of the above.

22. The element that helps hemoglobin reversibly bind with oxygen is

a. copper.

b. iodine.

c. iron.

d. magnesium.

e. manganese.

23. In a two pigment system for oxygen transport, the second pigment in the delivery chain normally has

a. lower oxygen affinity than the first pigment.

b. the same oxygen affinity as the first pigment.

c. higher oxygen affinity than the first pigment.

d. None of the above.

e. What was the question?

24. A person whose ventral respiratory group (in the medulla) had been destroyed would probably have difficulty with

a. inhalation of any kind.

b. exhalation of any kind.

c. resting breathing.

d. deeper breathing.

e. a and b.

25. Which of the following can pass through the blood-brain barrier by simple diffusion?

a. oxygen

b. carbon dioxide

c. H⁺

d. Two of the above. (a and b)

e. All of the above.

Short answer: Write a concise answer to each of the following questions. Your answers should fit in the spaces provided and should address only the question asked. Diagrams must be accompanied by written explanations. Each question is worth 6 points.

26. Describe the molecular events during cross-bridge cycling in a muscle. You may use the abbreviations “A” to indicate actin and “M” to indicate myosin. Be sure to include a written description of what is occurring, not just a diagram.

We’ll start with M and A bound in low energy state. An ATP binds to myosin, triggering the release of M from A. Myosin ATPase then hydrolyzes the ATP to ADP and P_i. These two molecules remain attached to the M, and the energy released converts M to the high energy conformation. The energized M is the form that can bind to A. When binding occurs, this triggers the change of M back to the low energy conformation as well as the release of the ADP and P_i. The energy released provides the power that pulls the M along the A as its conformation changes. This brings us back to the start.

27. The table below compares slow oxidative to fast glycolytic muscle fibers. Complete it for the characteristics indicated

	Fast glycolytic	Slow oxidative
Force production	High	Low
Mitochondrial density	Low	High
Myoglobin concentration	Low	High
Capillary density	Low	High
Glycogen stores	High	Low
Rate of fatigue	High	Low

28. Describe the pattern of electrical activity (i.e. action potentials) that occurs in the heart during a normal heartbeat cycle.  You do not need to discuss the particular channels or ions involved in changing membrane potentials or the mechanical results of these action potentials.

While all myocardial cells spontaneously depolarize, the cells that make up the sinoatrial node on the right atrium normally depolarize more rapidly than other cells, and hence are the first to reach threshold after the previous heartbeat. Once this depolarization triggers an AP in the SA node, the AP propagates to other cells of the atria through the gap junctions connecting cells. The AP’s also reaches the atrioventricular node, but does not spread directly to the ventricles. The AV node shows a delay of about 100 ms before depolarizing itself and triggering AP’s in the bundle of His. These AP’s then travel down the bundle to the Purkinje fibers and through these fibers to the contractile muscles of the ventricle.

29. Discuss the effects of epinephrine on the cardiovascular system. Be sure to include both the heart and blood vessels in your discussion.

Epinephrine affects the heart in two ways. First, it causes the SA node to depolarize more quickly, causing an increase in heart rate. Second, it causes the myocardium to contract more forcefully, causing an increase in stroke volume. Both of these effects result in an increase in cardiac output.

Epinephrine also affects vasodilation and constriction. Increasing levels of epinephrine cause vasoconstriction in most areas of the body, except in the muscles and heart, where is causes vasodilation. This pattern helps distribute blood flow in the most useful way for physical activity.

30. The graph below shows the oxygen saturation curves for human blood at a pH of 7.4 and 7.2.

a. Indicate on the graph which curve corresponds to which pH.
The left-hand curve is pH 7.4; the right is 7.2

b. What is the specific name for the shift caused by a drop in pH?
Bohr shift

c. Assuming normal hemoglobin at the lungs, how much oxygen (in precent) will be offloaded at tissues with a P_O2 of 30 torr

at pH 7.4: about 40% at pH 7.2: about 60%

d. What would the P_O2 have to be to get 50% saturation of the hemoglobin

at pH 7.4: about 25% at pH 7.2: about 35%

31. Imagine a person at rest holds her breath for 15 seconds and then begins breathing again. This breathing is both faster and deeper than normal until partial pressures in the lungs return to normal. Explain how breath holding for even a short period leads to increased ventilation afterwards.

If the breath is held, there is no exchange of oxygen or CO₂ in the alveoli with the atmosphere. As a result, levels of O₂ in the lungs and blood tend to decrease, while levels of CO₂ increase. While both these changes can affect ventilatory drive, CO₂ at lower levels of change. As CO₂ builds up, carbonic anhydrase facilitates its conversion to H⁺ and HCO₃^-. The resulting increase in H⁺ is sensed (over this timescale) by peripheral chemoreceptors, which pass this information along to the medulla. The medulla triggers increased ventilation (once breath holding ends) until CO₂ (and hence H⁺) levels return to normal.