Midterm 2 Key

Answers 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. Note – these instructions for the scantron are different than last time's.
   Fill in your scantron form as follows:  (1 point)
   • Write in your name in the upper left (last name first) and bubble it in.
   • If you wish to retrieve your exam score through the course web site and did not give me a PIN last time, write and bubble in a secret code (i.e. a PIN or password) in the “Special Codes” section.  Be sure you remember it!
   • Sign your form in the upper right.
      
   1. I actually read these new instructions and did what was asked.
   2. - e.  I only bubbled in the name of the anatomical location where you can stick this scantron.
   
    
2. Smooth muscle is most likely to be located in
   1. a postural muscle.
   2. an arm muscle.
   3. the tongue.
   4. the heart.
   5. an arteriole.
   
    
3. The term that describes an individual muscle cell is
   1. myofibril.
   2. muscle fiber.
   3. sarcomere.
   4. motor unit.
   5. filament.
   
    
4. Under normal conditions, the contraction of a muscle would involve action potentials traveling along which of the following?
   1. Motor neuron only
   2. Motor neuron and sarcolemma only
   3. Motor neuron, sarcolemma and t-tubule only
   4. Motor neuron, sarcolemma, t-tubule and sarcoplasmic reticulum only
   5. Motor neuron, sarcolemma, t-tubule, sarcoplasmic reticulum and sarcoplasm
   
    
5. The ion that controls cross-bridge cycling is
   1. sodium.
   2. potassium.
   3. chloride.
   4. iron.
   5. calcium.
   
    
6. If all the tropomyosin in a muscle were suddenly removed, which of the following would most likely happen?
   1. The muscle would immediately begin contracting, and would contract continuously until ATP ran out.
   2. The muscle would not contract until an action potential occurred, but then would contract continuously until ATP ran out.
   3. A rigor mortis like state would immediately occur, with the actin and myosin locked together.
   4. No contraction would be possible under any circumstances.
   5. The muscle would contract and stop contracting in the normal manner.
   
    
7. During cross-bridge cycling, the energy from ATP is used to
   1. break the bond between actin and myosin.
   2. create the bond between actin and myosin.
   3. energize actin, changing it to a high-energy conformation.
   4. energize myosin, changing it to a high-energy conformation.
   5. None of the above.
   
    
8. An experiment designed to examine an isotonic twitch contraction would allow you to measure which of the following variables?
   1. Force production
   2. Distance shortened
   3. Shortening velocity
   4. a and b
   5. b and c
   
    
9. In comparison to a twitch contraction, a tetanic contraction
   1. lasts longer
   2. generates more force
   3. has a shorter latent period
   4. a and b
   5. a, b and c
   
    
10. A muscle with a lot of mitochondria and relatively high contraction velocity is likely to be which type of muscle?
    1. Fast glycolytic
    2. Fast oxidative-glycolytic
    3. Slow oxidative
    4. Smooth
    5. None of the above
    
     
11. What type of blood vessel allows gas exchange between the blood and tissues?
    1. Arteries
    2. Arterioles
    3. Capillaries
    4. Venules
    5. Veins
    
     
12. Which of the following statements about the circulatory system is not true?
    1. One-way valves are located in some parts of the circulatory system to prevent blood from moving backwards.
    2. Some arteries carry deoxygenated blood.
    3. Blood pressure is higher in the systemic circulation than in the pulmonary circulation.
    4. Arteries are more elastic than other vessels.
    5. None of the above.
    
     
13. The brain receives its oxygen from blood passing through the
    1. carotid arteries.
    2. coronary arteries.
    3. subclavian arteries.
    4. hepatic arteries.
    5. iliac arteries.
    
     
14. The intercalated disks of the myocardium are important because they
    1. allow action potentials to spread from cell to cell.
    2. prevent backflow of blood.
    3. act as pacemakers.
    4. prevent tetanic contractions.
    5. control calcium flow.
    
     
15. During a heartbeat, the aortic valve closes when
    1. blood pressure in the ventricles becomes greater than blood pressure in the atria.
    2. blood pressure in the atria becomes greater than blood pressure in the ventricles.
    3. blood pressure in the ventricles becomes greater than blood pressure in the arteries.
    4. blood pressure in the arteries becomes greater than blood pressure in the ventricles.
    5. The aortic valve never closes.
    
     
16. Heart rate is strongly influenced by all of the following except
    1. the volume of blood entering the ventricles.
    2. the sympathetic nervous system.
    3. the parasympathetic nervous system.
    4. epinephrine
    5. All of the above strongly influence heart rate.
    
     
17. The total volume of blood flow per minute is greatest through which of the following parts of the circulatory system?
    1. The heart
    2. All arteries combined
    3. All capillaries combined
    4. All veins combined
    5. The same amount of blood per minute flows through all of these.
    
     
18. If a particular arteriole decreases in diameter by one-half, the blood flow through that arteriole will
    1. decrease 4×
    2. decrease 16×
    3. increase 2×
    4. increase 4×
    5. increase 16×
    
     
19. During a deep inhalation, the lungs expand because
    1. the negative pressure of the intrapleural fluid keeps the lungs "stuck" to the expanding walls of the thorax.
    2. the volume of the anatomical dead space decreases.
    3. the pharynx acts as a positive pressure pump to force air into the lungs.
    4. the compliance of the lungs tends to make them expand as the intercostal muscles are relaxed.
    5. the pulmonary stretch receptors get activated.
    
     
20. The term used to refer to the amount of air drawn into the lungs with each breath is
    1. stroke volume.
    2. minute ventilation.
    3. alveolar ventilation.
    4. tidal volume.
    5. ventilation frequency.
    
     
21. Anatomical dead space includes all of the following except
    1. the trachea
    2. the bronchi
    3. the bronchioles
    4. All of the above are part of the anatomical dead space.
    5. None of the above is part of the anatomical dead space.
    
     
22. If the solubility of a gas X is .5 ml/liter·torr and the concentration of the gas in a sample of water is 5 ml/liter, then the partial pressure of X in the water is
    1. 0.1 torr
    2. 2.5 torr
    3. 5 torr
    4. 10 torr
    5. Impossible to tell with the information provided.
    
     
23. Blood returning to the lungs in a person at rest would likely show which of the following gas partial pressures?
    1. P_O2 = 40 torr, P_CO2 = 40 torr
    2. P_O2 = 40 torr, P_CO2 = 46 torr
    3. P_O2 = 40 torr, P_CO2 = 104 torr
    4. P_O2 = 104 torr, P_CO2 = 40 torr
    5. P_O2 = 104 torr, P_CO2 = 46 torr
    
     
24. In a two pigment system involving myoglobin,
    1. the myoglobin has a lower affinity for oxygen than the hemoglobin and passes oxygen to the hemoglobin.
    2. the myoglobin has a higher affinity for oxygen than the hemoglobin and passes oxygen to the hemoglobin.
    3. the hemoglobin has a lower affinity for oxygen than the myoglobin and passes oxygen to the myoglobin.
    4. the hemoglobin has a higher affinity for oxygen than the myoglobin and passes oxygen to the myoglobin.
    5. the hemoglobin and myoglobin share the oxygen equally.
    
     
25. If carbon dioxide levels rise in the lungs, then the hydrogen ion levels in the blood
    1. will drop because additional bicarbonate ions are formed (via carbonic anhydrase), and this is a base that eliminates hydrogen ions.
    2. will rise because carbon dioxide binds to bicarbonate ions.
    3. will rise because the formation of bicarbonate ions also creates hydrogen ions.
    4. will drop because more carbon dioxide will be dissolved in the blood rather than forming carbonic acid.
    5. will remain constant.
    
     
26. The particular set of cells that drives the respiratory rhythm is the
    1. medullary respiratory neurons.
    2. medullary inspiratory neurons.
    3. medullary inflationary neurons.
    4. medullary expiratory neurons.
    5. medullary explanatory neurons.
    
     

Short answer:   Write a concise answer to each of the following questions.  Your answers should fit in the spaces provided.  Each question is worth 4 points.

27. As a contracting sarcomere shortens from about 3.6 to 2.25 µm in length, force production increases steadily. But during shortening from 2.25 to 2 μm, force production stops increasing.  Why is this?

    As the sarcomere shortens from 3.6 to 2.25 µm, more and more myosin heads can attach to the thin filaments.  At 2.25 µm, the actin filaments start overlapping the "bald spot" of the thick filaments, and no additional cross-bridges are forming as the sarcomere continues to shorten to 2.0 µm.
     

28. What is a motor unit?

    A motor unit is all the muscle fibers attached to a single motor neuron.  They are all activated at the same time.
     

29. What is active hyperemia, and how does it work?

    Active hyperemia is a process in which local effects act to increase blood flow to a particular region.  When CO₂ and H⁺ levels increase and O₂ levels decrease, the endothelium of blood vessels (especially arterioles) in the region release nitric oxide.  The nitric oxide diffuses into the smooth muscle layer of the vessels, causing them to relax, thus increasing their diameter and allowing more blood through.
     

30. What would be the likely effect of abnormally high blood pressure on the rate of lymph formation (assuming all other variables are unaffected)?  Why?

    An increase in hydrostatic pressure would increase the rate of bulk flow, or ultrafiltration, of fluid out of the capillaries.  Since the osmotic pressures are unchanged, this would mean a greater net loss of fluid from the capillaries, and hence a greater rate of lymph formation.
     

31. Recall that there is generally little ventilatory response to a drop in arterial P_O2 until levels reach about 60 torr.  Why is a ventilatory response relatively useless at higher P_O2's?

    Above P_O2 = 60 torr, the hemoglobin is still almost completely saturated with oxygen.  Therefore there is no real decrease in the ability of the blood to deliver O₂ at partial pressures greater than 60.  An increase in ventilation would increase the P_O2, but this would not cause the blood to carry any more oxygen.
     

32. On the graph below, draw in a line showing the possible shape of the oxygen saturation curve after a shift due to the Bohr effect takes place, then answer the questions that follow.
     

1. If the P_O2 at the lungs is 104 torr and the P_O2 in a particular set of tissues is 30 torr, about what percentage of the oxygen carried by the hemoglobin will be unloaded at these tissues before the Bohr shift?

   About 40%.
    

2. How much more oxygen will be unloaded after the Bohr shift (as you drew it) takes place?

   About 15% more (in this case).