Midterm 2 Key

Answers are in italics

Multiple choice: As always, choose the best answer for each multiple-choice question. Answer on your scantron form. Each question (except 1) is worth 3 points.

1. Fill in your scantron form as follows: (1 point)
   • Write and bubble in your social security number in the lower left.
   • If you wish to retrieve your exam score through the course web site, write and bubble in a secret code in the “Special Codes” section. Be sure you remember it!
   • Write in your name in the upper left (last name first). (No bubbling required)
   • Sign your form in the upper right.
   1. Done!
   2. – e. I don't want your stinking point!
       
2. Cardiac muscle is a type of
   1. smooth muscle.
   2. skeletal muscle.
   3. striated muscle.
   4. anaerobic muscle.
   5. More than one of the above.
       
3. The component of muscle cells that actively generates force during contraction is the
   1. thin filaments.
   2. thick filaments.
   3. Z-line.
   4. sarcoplasmic reticulum.
   5. mitochondria.
       
4. As a sarcomere is stretched from about 2.25 to 3 microns, the force the sarcomere generates during contraction
   1. increases because of elastic forces in the sarcomere.
   2. increases because more myosin heads overlap with actin.
   3. decreases because of the increased load on the sarcomere.
   4. decreases because fewer myosin heads overlap with actin.
   5. stays the same because none of the above factors changes.
       
5. Which of the following is most directly responsible for opening Ca²⁺ channels in the sarcoplasmic reticulum?
   1. Ryanodine receptors
   2. Transverse tubules
   3. Dihydropyridine receptors
   4. Acetocholine
   5. The sarcolemma
       
6. Which of the following best describes the working of the troponin-tropomyosin system?
   1. Ca²⁺ binds to globular actin, allowing myosin heads to bind to the troponin-tropomyosin complex.
   2. Ca²⁺ binds to tropomyosin, moving troponin so that myosin heads can bind to the troponin-actin complex.
   3. Ca²⁺ binds to troponin, moving tropomyosin so that myosin heads can bind to the tropomyosin-actin complex.
   4. Ca²⁺ binds to tropomyosin, moving troponin so that myosin heads can bind to actin.
   5. Ca²⁺ binds to troponin, moving tropomyosin so that myosin heads can bind to actin.
       
7. A muscular contraction involving a single action potential and the muscle held at fixed length would be called an
   1. isotonic twitch contraction.
   2. isotonic tetanic contraction.
   3. isometric twitch contraction.
   4. isometric tetanic contraction.
   5. None of the above.
       
8. The delay between excitation and the start of muscle shortening
   1. increases as the load on a muscle increases.
   2. remains constant as the load on a muscle increases.
   3. decreases as the load on a muscle increases.
   4. is defined as the contraction velocity.
   5. Two of the above.
       
9. The collection of muscle fibers innervated by a single motor neuron are referred to as
   1. a motor unit
   2. a myofibril
   3. glycolytic fibers
   4. a sarcomere
   5. a sarcolemma
       
10. Which type of blood vessel would be most associated with strongly pulsatile flow?
    1. Arteries
    2. Arterioles
    3. Capillaries
    4. Venules
    5. Veins
        
11. Which of the following statements is true?
    1. Most of the blood volume is located in the arteries and arterioles.
    2. Most of the blood volume is located in the capillary beds.
    3. Most of the blood volume is located in the veins and venules.
    4. The blood volume in the arteries and arterioles is roughly equal to that in the veins and venules.
    5. b. and d. are true.
        
12. The subclavian artery(ies) supplies blood to
    1. the head
    2. the arms
    3. the liver
    4. the kidneys
    5. the legs
        
13. The atrioventricular node of the heart
    1. controls blood flow between the atrium and ventricle.
    2. controls blood flow between the ventricle and aorta.
    3. initiates the heartbeat.
    4. acts to provide a delay between the atrial and ventricular contractions.
    5. is activated by the bundle of His.
        
14. Which of the following events occurs soonest after the beginning of diastole?
    1. The aortic valve closes.
    2. The aortic valve opens.
    3. The atrial valve closes.
    4. The atrial valve opens.
    5. The ventricles contract.
        
15. Which of the following statements is true?
    1. Blood flow rate (ml/min) is higher in the systemic system than in the pulmonary system, but blood pressure is the same in both systems.
    2. Blood flow rate (ml/min) is higher in the pulmonary system than in the systemic system, but blood pressure is the same in both systems.
    3. Blood pressure is higher in the systemic system than in the pulmonary system, but blood flow rate (ml/min) is the same in both systems.
    4. Blood pressure is higher in the pulmonary system than in the systemic system, but blood flow rate (ml/min) is the same in both systems.
    5. Blood flow rate (ml/min) and blood pressure are the same in both systemic and pulmonary systems.
        
16. Cardiac output is defined as
    1. the amount of oxygen carried by the blood.
    2. the amount of carbon dioxide carried by the blood.
    3. the number of heartbeats per minute.
    4. the blood volume moved by one beat of the heart.
    5. the amount of blood circulated by the heart per minute.
        
17. Which of the following does not typically serve to control arteriole diameter?
    1. Sympathetic innervation
    2. Parasympathetic innervation
    3. Epinephrine
    4. Active hyperemia
    5. All of the above serve to control arteriole diameter.
        
18. Which of the following statements best describes the relationship between hydrostatic pressure and osmotic pressure in a capillary?
    1. Hydrostatic and osmotic pressure are equal along the capillary.
    2. Hydrostatic pressure in the capillary is always greater than the osmotic pressure.
    3. Osmotic pressure in the capillary is always greater than hydrostatic pressure.
    4. Hydrostatic pressure decreases along the capillary while osmotic pressure remains constant.
    5. Osmotic pressure decreases along the capillary while hydrostatic pressure remains constant.
        
19. Gas exchange in the lungs takes place at
    1. the trachea.
    2. the bronchi.
    3. the bronchioles.
    4. the alveoli.
    5. more than one of the above.
        
20. Exhalation
    1. relies on a forced pressure pump to move air out of the lungs by diffusion.
    2. relies on a forced pressure pump to move air out of the lungs by bulk flow.
    3. relies on a suction pump to move air out of the lungs by diffusion.
    4. relies on a suction pump to move air out of the lungs by bulk flow.
    5. does not rely on pressure to move air out of the lungs.
        
21. Which of the following statements best describes the events involved in ventilation at rest?
    1. Rhythmic patterns generated by the medullary expiratory neurons control breathing.
    2. Exhalation depends on the activation of the internal intercostal muscles.
    3. Exhalation depends on the activation of the diaphragm.
    4. Inhalation depends on the activation of the external intercostal muscles.
    5. Inhalation depends on the activation of the diaphragm.
        
22. The approximate composition of the gas in the alveoli at rest is
    1. P_O2 = 14 torr, P_CO2 = 5 torr, P_H2O = 0 torr
    2. P_O2 = 14 torr, P_CO2 = 5 torr, P_H2O = 6 torr
    3. P_O2 = 104 torr, P_CO2 = 40 torr, P_H2O = 0 torr
    4. P_O2 = 104 torr, P_CO2 = 40 torr, P_H2O = 47 torr
    5. P_O2 = 160 torr, P_CO2 = 1 torr, P_H2O = 0 torr
        
23. The air volume in the anatomical dead space of the human respiratory tract
    1. is about 500 ml.
    2. is trapped in place and never moves.
    3. occupies areas where diffusion of gases does not take place.
    4. influences the alveolar ventilation rate.
    5. More than one of the above. [c and d are correct]
        
24. Diffusion of a gas is always driven by
    1. the gas's fractional content.
    2. the gas's concentration.
    3. the gas's partial pressure.
    4. the gas's solubility.
    5. the gas's joie de vie.
        
25. Use the graph below and your knowledge of the oxygen carrying capacity of blood to answer the following questions. About how much oxygen would be carried by the blood at P_O2 = 30 torr?
    1. 30 ml/liter
    2. 60 ml/liter
    3. 90 ml/liter
    4. 120 ml/liter
    5. 200 ml/liter
        
26. The Bohr effect
    1. causes a right-shift in the oxygen saturation curve.
    2. significantly reduces the saturation of hemoglobin with oxygen in the lungs.
    3. results from changes in blood temperature.
    4. is primarily important during rest.
    5. is the most Bohr-ing subject ever.
        
27. If you began breathing into and out of a plastic bag, so that carbon dioxide built up and oxygen levels were reduced, which of the following would likely occur first?
    1. Increases in H⁺ levels sensed directly by the medulla would lead to increased ventilation rates.
    2. Increases in H⁺ levels sensed by the carotid and aortic bodies would lead to increased ventilation rates.
    3. Decreases in oxygen levels sensed directly by the medulla would lead to increased ventilation rates.
    4. Decreases in oxygen levels sensed by the carotid and aortic bodies would lead to increased ventilation rates.
    5. Ventilation rates would not be affected by this situation.

Short answer: Write a concise answer to each of the following questions. Your answers should fit in the spaces provided. Each question is worth three points.

28. In the diagram below of the crossbridge cycle in a muscle, indicate the state of actin, myosin, and ATP/ADP at points a, b, and c. You can use symbols or words in your explanation, but be sure to indicate what any new symbols (such as “*”; hint, hint) indicate.

    Symbols used A = actin M = myosin · = bound together + = not bound

    There are a number of acceptable answers here, in terms of both the particular steps given as answers and the form of the answer. An example is:

    1. A • M • ADP • P_i
    2. A + M • ATP
    3. A • M* • ADP • P_i
        
29. On the graph provided, draw in the general relationship between the shortening velocity of a muscle and the load placed on that muscle, during a twitch contraction. What values do the x-intercept and y-intercept indicate?
    The x-intercept indicate the maximum force (or tension) the muscle can generate.
    The y-intercept indicates the maximum shortening velocity of the muscle under no load.
     
30. What is the difference between a twitch and tetanic muscle contraction, and what is the relative force produced by the second relative to the first?
    
    A twitch contraction is the result of a single action potential, while a tetanic contraction results from a continuous series of action potentials. Tetanic contractions are about three (two to four) times as strong as a twitch contraction.
     
31. Fill in the appropriate relative values (e.g. fast/slow, few/many, etc.) in the following table describing the characteristics of different muscle types:
    
    

    	Slow Oxidative	Fast Oxidative- Glycolytic	Fast Glycolytic
    Contraction Velocity	Slow	Fast	Fast
    Myoglobin content	High	High	Low
    Rate of fatigue	Low	Intermediate	High

     
32. What is the origin of lymph?
    
    Lymph is the ultrafiltrate produced when plasma is forced between the endothelial cells of the capillaries.
     
33. Cardiac hypertrophy (thickening of the ventricular walls) can cause a decrease in the stroke volume of the heart. If cardiac output must be maintained at normal levels, what response in the heart or vascular system might maintain CO despite the decrease in stroke volume, and why?
    
    Since cardiac output is the product of stroke volume and heart rate. Therefore one way to counteract a decrease in stroke volume would be to increase heart rate.
     
34. What are the three major forms of carbon dioxide transport in the blood, and about what percent of the total CO₂ is carried in each form?
     
    • Bicarbonate ion: ~70%
    • Carbamino compounds: ~23%
    • Dissolved in plasma: ~7%