MCB 136 — 2nd Mid-Term. Mean: 70.55 Std Dev: 12.47
True-False. Indicate clearly with T or F. (1 pt each)
T 1. Cutting the vagus nerve causes the heart to speed up.
F 2. In a person with a normal heart, end diastolic volume is equal to 150 ml and stroke volume is also 100 ml.
F 3. Cardiac action potentials proceed in the sequence: SA node, atria, bundle of His, AV node, ventricles, papillary muscles
F 4. Cardiac action potentials are longer in duration and larger in magnitude in the SA node compared to those in the ventricular musculature.
F 5. Ryanodine receptors are transmembrane proteins in the T-tubules of cardiac and skeletal muscle.
T 6. Although the left and right ventricles have different shapes and thicknesses, they contract at the same rates and have the same stroke volumes.
F 7. The cardiovascular center that controls autonomic nerves to the heart is located in the hypothalamus.
T 8. The compliance of the veins is larger than that of the arteries.
T 9. Constriction of the veins causes increased venous return but only a small (<30%) increase in total peripheral resistance.
F 10. The efficiency of muscle contraction (force/ATP utilized) is in the order skeletal > cardiac > smooth.
T 11. Myosin light chain phosphatase and ATP are both important for relaxation of smooth muscle, but not skeletal or heart muscle.
F 12. The systemic veins contain roughly 300 ml at any one time.
T 13. Velocity of blood flow is faster in the aorta than that in the systemic capillaries.
T 14. Resistance to blood flow through a single capillary is larger than that through an artery of the same length.
15. Arterial hypoxemia (i.e., decreased arterial PO2) is a consequence of:
F low hemoglobin concentration.
T living at high altitude.
T ventilation-perfusion maldistribution in the lungs.
T hypoventilation.
16. Movement of fluid out of pulmonary capillaries:
T is increased if surfactant is deficient.
T is an entirely normal phenomenon.
F implies movement of fluid into the alveolar spaces.
T is necessarily increased in rate by an increase in pulmonary capillary pressure.
F is necessarily increased in rate by an increase in pulmonary blood flow.
Multiple Choice. Circle the one best answer. 2 pts each
1. Which of the following causes Na channels in heart muscle to open?
a. hyperpolarization
b. depolarization
c. increases in cell Ca
d. activation of the acetylcholine receptor
e. epinephrine
2. Which of the following is phosphorylated during sympathetic stimulation of the heart?
a. myosin light chain
b. actin
c. ryanodine receptor
d. Ca ATPase-pump
e. phospholamban
3. Which functions would be most affected by a blocker of the IP3 receptor?
a. skeletal muscle contraction
b. cardiac muscle contraction
c. smooth muscle contraction
d. release of neurotransmitter by sympathetic nerves
e. release of neurotransmitter by parasympathetic nerves
4. What is the approximate duration of a ventricular action potential?
a. about 2 msec
b. about 20 msec
c. about 200 msec
d. about 1 sec
5. Which of the following is found in the plasma membrane of cardiac muscle but not skeletal muscle?
a. Na/K-ATPase
b. Na/Ca exchange
c. Ca-ATPase/pump
d. V-sensitive Na channel
e. phospholamban
6. Which of the following chemicals causes contraction of smooth muscles surrounding arterioles supplying skeletal muscles?
a. epinephrine
b. norepinephrine
c. nitric oxide
d. adenosine
e. CO2
7. During exercise cardiac output increases by up to five fold, but arterial blood pressure remains roughly constant. This is caused by:
a. shunting of blood from muscles to the GI tract
b. dilation of capillaries
c. increased venous return
d. relaxation of arteriolar smooth muscle
e. activation of the "muscle pump"
8. Which of the following is false?
a. The trachea is surrounded by rings of cartilage.
b. The area of the conductive zone exceeds that of the respiratory zone in the lung.
c. The intrapleural space lies between the lung and the chest wall.
d. Both squamous and cuboidal epithelial cells line the alveoli.
9. Which of the following is NOT necessary for tidal (normal) ventilation?
a. Contraction of the diaphragm.
b. Relaxation of the diaphragm.
c. Recoil of the chest cavity.
d. Change in translung pressure.
e. Active contraction of the intercostals.
10. In order to decrease the PCO2 in the alveoli, one can:
a. Take small rapid breaths without changing the minute volume.
b. Increase metabolism without changing breathing rate or minute volume.
c. Increase metabolism and increase breathing rate without changing the minute volume.
d. Decrease metabolism without changing breathing rate or minute volume.
11. The change in lung volume in response to a given transpulmonary pressure gradient is used as a measure of C (V, vital capacity; C, compliance; A, airway resistance), which will be D by the absence of surfactant and D by the investment of fibrotic connective tissue in the alveoli (I, increased; D, decreased).
a. C, D, D
b. C, I, D
c. V, D, D
d. V, I, D
e. A, D, I
f. A, D, D
12. A subject is breathing with a tidal volume of 0.5 liters, a dead space of 0.15 liter and a frequency of 10 breaths/min, so that his total minute volume is 5 liters/min. He then changes his breathing pattern to a tidal volume of 0.3 liter, a frequency of 20/min, and a total minute volume of 6 liters/min. Assuming no change in dead space, this would affect alveolar ventilation as follows:
a. increase by 1 liter/min
b. increase by 0.5 liter/min
c. no change
d. decrease by 0.5 liter/min
e. decrease by 1 liter/min
13. Each of the following may impair alveolar gas diffusion EXCEPT
a. decreased interstitial pulmonary osmotic pressure
b. pneumothorax
c. fibrous scarring of alveolar wall
d. increase in physiologic dead space
e. pneumonia
14. Which of the following is not a difference between the systemic and pulmonary circulatory systems?
a. The systemic system has higher compliance.
b. Hypoxia causes dilation of blood vessels in the systemic circulation, but constriction in the pulmonary circulation.
c. Resistance is lower in the pulmonary circulation.
d. Arterial pressure is higher in the systemic circulation.
15. Ablation of which of the following would decrease the blood's carbon dioxide carrying capacity?
a. carbonic anhydrase
b. anion exchanger
c. acid dismutase
d. A and B
e. A, B, and C
16. Which of the following best describes the effect of lowered pH on hemoglobin?
a. It decreases the O2-carrying capacity of the blood.
b. It increases the O2-carrying capacity of the blood.
c. It increases the affinity of Hb for O2.
d. It decreases the affinity of Hb for O2.
17. 2,3-DPG has a greater affinity for A (M: myoglobin, A: adult hemoglobin, F: fetal hemoglobin) and, when it binds, it stabilizes a conformation that has L (G, greater; L, less) affinity for oxygen.
a. M, G
b. M, L
c. A, G
d. A, L
e. F, G
f. F, L
18. Medullary (central) chemoreceptors are exquisitely sensitive to acute alterations of arterial PCO2 (PO2; pH; PCO2) and as a result will produce a change in AV (AV, alveolar ventilation; PP, pulmonary perfusion).
a. PO2, AV
b. pH, AV
c. PCO2, AV
d. PO2, PP
e. pH, PP
f. PCO2, PP
19. Hypoxia influences respiration primarily through its stimulatory effect
a. directly on the respiratory centers
b. directly on the lungs
c. on the medullary chemoreceptors
d. on the carotid and aortic chemoreceptors
e. directly on the Hb-O2 dissociation curve
MATCHING
1. (DELETED)
2. Select the most appropriate curve to describe the relationships indicated below: (curves may be used more than once. (6 pts)
|
Curve |
X-axis |
Y-axis |
| C | time in pulmonary capillary |
pulmonary capillary PCO2 |
| D | flow in a stiff cylindrical tube |
driving pressure |
| C | arterial PO2 |
alveolar ventilation |
| C | alveolar ventilation |
alveolar PCO2 |
| B or C | pressure in alveolus at constant wall tension |
radius of alveolus |
3. Insert the letter best describing the O2 conditions for each of the following:
For example, in pulmonary edema or pneumonia, alveloar PO2 would be normal, but because of the diffusion barrier arterial PO2 would be lower than normal, as would all of the subsequent compartments. Therefore, the answer to condition #1 would be C. (4 pts)
C 1) Pulmonary edema and pneumonia
A 2) Cyanide in drink
D 3) Heart failure
E 4) Hemorrhage
B 5) Vacation in The Rockies
| A |
B |
C |
D |
E | |
| Alveolar PO2 |
Normal |
Low |
Normal |
Normal |
Normal |
| Arterial PO2 |
Normal |
Low |
Low |
Normal |
Normal |
| HbO2 saturation |
Normal |
Low |
Low |
Normal |
Normal |
| Art. O2 content |
Normal |
Low |
Low |
Normal |
Low |
| Venous PO2 |
High |
Low |
Low |
Low |
Low |
Short Answer and Calculations
1. a. (DELETED)
1. b. Draw the ventricular muscle action potential and describe the ion channel mechanisms that assure that sympathetic stimulation will not elicit tetanic contraction. (3 pts)
Plateau gives an increase in refractory period due to a decrease in gK+ and an increase in gCa++.
The Na+ channel is inactivated until repolarization. Twitch force corresponds with A.P.
2. a. Using Poiseuille's law, calculate the relative resistance to blood flow through the arterioles vs the veins in a person with blood pressure of 120 mmHg/80 mmHg. (4 pts)
DP = F x R
DParteriole = (100 - 25) mmHg
DPvein = (15 - 0) mmHg
F = 5 L / min for each
Rarteriole = (75 mmHg) / (5 L / min)
Rvein = (15 mmHg) / (5 L / min)
Therefore, Rarteriole / Rvein = 5
2. b. What would happen to resistance through the arterioles when sympathetic nerves are stimulated — increase, decrease or no change? (1 pt) Explain. (2 pts)
Overall, the resistance increases because sympathetic stimulation causes a constriction of arterioles and R is proportional to r- 4. (If you said decrease, and said that it was because r increased (arterioles dilated), you received credit if you correctly identified tissues that these specific dilating arterioles serve.)
3. Explain how cardiac glycosides alter the heart's contractility? (4 pts)
Cardiac glycosides (ouabain, digitalis) inhibit the Na,K-ATPase. This causes a decrease in the Na gradient because less is extruded by the pump. As a result, the activity of the Na/Ca exchanger is decreased because it uses the Na gradient to remove Ca from the cytoplasm. Therefore, cells have elevated cytosolic Ca, which leads to increased contractility in cardiac muscle.
4. During hemorrhage arterial blood pressure decreases.
a. What happens to action potential frequency in the nerves from the baroreceptors to the cardiovascular center — increase, decrease or no change? (1 pt)
Decrease.
b. What is the neurotransmitter released by sympathetic nerves onto the heart? (1 pt)
Norepinephrine.
c. Explain why reduced blood pressure alters hematocrit. (4 pts)
Decreased arterial blood causes a decrease in capillary blood pressure; osmotic pressure is constant; therefore, an increase in reabsorption and a decrease in filtration of fluid in the capillary leads to a decrease in hematocrit (same RBC, more fluid).
e. Explain how sympathetic-induced venoconstriction increases cardiac output. (3 pts)
An increase in venoconstriction and the presence of valves causes an increase in blood flow to the heart (increased venous return). An increase in EDV causes an increase in SV; increased SV x hbr = increased CO.
5. A Wiggers diagram is shown below (NOT!).
a. Calculate cardiac output. (2 pts)
CO = (EDV - ESV) x hbr = (135 mL - 65 mL) x (1 beat / 0.8 s)
= (70 mL / 0.8 s) x (60 s / min) = 5250 mL / min
b. When does isovolumetric contraction for the ventricles occur? A-B; B-C; C-D; or D-A? (1 pt.)
A- B
c. When does the aortic valve shut? A, B, C, or D? (1 pt)
C
6. Given the following data:
| PCO2 expired air | 28 mm Hg | |
| PCO2 alveolar air | 42 mm Hg | |
| respiratory rate | 14 breaths/min | |
| Tidal volume | 0.6 L | |
| Inspiratory reserve volume | 2.8 L | |
| Expiratory reserve volume | 1.0 L | |
| Residual volume | 1.2 L |
Calculate: (10 pts)
a. Vital capacity
VT + IRV + ERV = 0.6 L + 2.8 L + 1.0 L = 4.4 L
b. Functional residual capacity
ERV + RV = 1.0 L + 1.2 L = 2.2 L
c. Total lung capacity
VC + RV = 4.4 L + 1.2 L = 5.6 L
d. Dead space
VD = VT [PACO2 - PECO2] / PACO2
= 0.6 L [42 mmHg - 28 mmHg] / 42 mmHg = 0.2 L
e. Alveolar ventilation rate
Va = f (VT - VD) = (14 / min) x (0.6 L - 0.2 L) = 5.6 L