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Inquiry Questions

FIGURE 44.20
The relationship between air pressure and altitude above sea level. At the high altitudes characteristic of mountaintops, air pressure is much less than at sea level. At the top of Mount Everest, the world's highest mountain, the air pressure is only one-third that at sea level.
What is the difference in percentage of oxygen between Mount Everest and Mount Whitney?
Answer: The percentage of oxygen is the same whether on Mt. Everest or Mt. Whitney; a percentage of 20.95. However, there are fewer air molecules present at the altitudes of Mt. Everest and so the partial pressure of oxygen is smaller (260 mmHg x 20.95% = 54 mmHg) compared to the partial pressure of oxygen at Mt. Whitney (500 mmHg x 20.95% = 104 mmHg).
FIGURE 44.32
The oxyhemoglobin dissociation curve. Hemoglobin combines with O2 in the lungs, and this oxygenated blood is carried by arteries to the body cells. After oxygen is removed from the blood to support cellular respiration, the blood entering the veins contains less oxygen.
How would you determine how much oxygen was unloaded to the tissues?
Answer: The difference in oxygen content between arteries and veins during rest and exercise shows how much oxygen was unloaded to the tissues.
FIGURE 44.33
The effect of pH and temperature on the oxyhemoglobin dissociation curve. (a) Lower blood pH and (b) higher blood temperatures shift the oxyhemoglobin dissociation curve to the right, facilitating oxygen unloading. In this example, this can be seen as a lowering of the oxyhemoglobin percent saturation from 60% to 40%, indicating that the difference of 20% more oxygen is unloaded to the tissues.
What effect does high blood pressure have on oxygen unloading to the tissues during exercise?
Answer: It increases it. At any pH or temperature, the percentage of O2 saturation falls (e.g. more O2 is delivered to tissues) as pressure increases.

Self Test

1). Which of the following statements is false?
    a). Only arteries carry oxygenated blood.
    b). Both arteries and veins have a layer of smooth muscle.
    c). Both arteries and veins branch out into capillary beds.
    d). Precapillary sphincters regulate blood flow through capillaries.
Answer: a

2). The lymphatic system is like the circulatory system in that they both
    a). have nodes that filter out pathogens.
    b). have a network of arteries.
    c). have capillaries.
    d). are closed systems.
Answer: c

3). A molecule of CO2 that is generated in the cardiac muscle of the left ventricle would not pass through which of the following structures before leaving the body?
    a). right atrium
    b). left atrium
    c). right ventricle
    d). left ventricle
Answer: b

4). In vertebrate hearts, atria contract from the top, while ventricles contract from the bottom. How is this accomplished?
    a). The depolarization from the sinoatrial node proceeds across the atria from the top, while the depolarization from the atrioventricular node is carried to the bottom of the ventricles before it emanates over the ventricular tissue.
    b). The depolarization from the sinoatrial node is initiated from motor neurons coming down from our brain, while the depolarization from the atrioventricular node is initiated from motor neurons coming up from our spinal cord.
    c). Gravity carries the depolarization from the sinoatrial node down from the top of the heart, while contraction of the diaphragm forces the depolarization from the atrioventricular node to move from the bottom up.
    d). This statement is false; both contract from the bottom.
Answer: a

5). Throughout evolution, natural selection has favored changes that optimize respiration mechanisms in animals. According to Fick's Law, which of the following changes would optimize the rate of diffusion, R?
    a). decrease the surface area, A, over which diffusion takes place
    b). increase the distance, d, over which diffusion takes place
    c). increase the concentration difference, p, between the interior of the organism and the external environment
    d). increase the diffusion constant, D
Answer: c

6). Which type of circulatory system regulation do some vertebrates employ to maintain body temperature in a cold environment?
    a). concurrent exchange
    b). countercurrent exchange
    c). vasodilation
    d). nitric oxide production
Answer: b

7). What is the stroke volume of a woman with a heart rate of 66 beats/minute and a cardiac output of 4.7 liters/minute?
    a). 310 milliliters/beat
    b). 14 milliliters/beat
    c). 70 milliliters/beat
    d). 71 milliliters/beat
Answer: d

8). If the total pressure of gas dissolved in blood plasma is 120 mm Hg, what is the partial pressure of nitrogen in the plasma? (Recall that air contains approximately 78% nitrogen.)
    a). 94 mm Hg
    b). 42 mm Hg
    c). 22 mm Hg
    d). 78 mm Hg
Answer: a

9). When you take a deep breath, your stomach moves out because:
    a). swallowing air increases the volume of the thoracic cavity.
    b). your stomach shouldn't move out when you take a deep breath because you want the volume of your chest cavity to increase, not your abdominal cavity.
    c). contracting your abdominal muscles pushes your stomach out, generating negative pressure in your lungs.
    d). when your diaphragm contracts, it moves down, pressing your abdominal cavity out.
Answer: d

10). If you hold your breath for a long time, body CO2 levels are likely to ____________, and the pH of body fluids is likely to _____________.
    a). increase; increase
    b). decrease; increase
    c). increase; decrease
    d). decrease; decrease
Answer: c

Test Your Visual Understanding

1). The Bohr effect describes the effect of pH on hemoglobin's affinity for oxygen. This figure shows a standard oxyhemoglobin dissociation curve. Draw a curve that represents the effect of a low pH according to the Bohr effect.
Answer: The drawn line should represent the curve for pH 7.2 found in figure 44.33a.

Apply Your Knowledge

1). Tissue plasminogen is an enzyme that, when activated, breaks down fibrin. How might the drug tissue plasminogen activator, t-PA, help to reduce the damage caused by strokes and heart attacks?
Answer: Heart attacks are very often caused by a blockage that inhibits the passage of blood through the coronary arteries. Similarly, a stroke is caused by an interference with the blood supply from the brain. In both of these cardiovascular diseases, a blood clot may be the involved in the restriction of blood flow. The drug t-PA may help reduce the damage by breaking down fibrin present in blood clots, thereby restoring blood flow.

2). Dr. Hearthealth is so impressed with your knowledge of cardiovascular physiology that he asks you to help with a particularly difficult case. He proceeds to tell you that his patient has a prolonged PQ wave in their electrocardiogram (ECG), which you know means that the delay between the atrial contraction and ventricle contraction is too long. What heart structure is likely causing this problem? Why?
Answer: The atrioventricular node provides the only pathway for the conduction of the depolarization from the atria to the ventricles. If the atrioventricular node is not functioning properly it may lead to an increased delay between the atrial contraction and ventricle contraction.

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