40. Circulatory System

When you hold your breath, which of the following first leads to the urge to breathe?

a. Falling CO₂

b. Falling O₂

c. Falling pH of the blood

d. Rising pH of the blood

Which of the following promotes oxygen release from hemoglobin?

a. A decrease in temperature

b. An increase in O₂ level.

c. A decrease in pH

d. A decrease in carbonic anhydrase activity

When you hold your breath, which of the following blood gas changes first leads to the urge to breathe?

a. Rising O₂

b. Falling O₂

c. Rising CO₂

d. Falling CO₂

Countercurrent gas exchange in the gills of a fish

a. Maintains a gradient that enhances diffusion.

b. Enables the fish to obtain oxygen without swimming.

c. Means that blood and water flow at different rates.

d. Allows O₂ to diffuse against its partial pressure gradient.

When you inhale, the diaphragm

a. Relaxes and moves upward.

b. Relaxes and moves downward.

c. Contracts and moves upward.

d. Contracts and moves downward.

Explain how each parameter in Fick's law of diffusion is reflected in the structure of the mammalian lung.

Frog lungs have a smaller surface area for gas exchange than mammalian lungs. How do frogs compensate for this difference?

a. Frog tissue absorbs more oxygen from the blood than mammalian tissue does.

b. Frogs breathe more quickly than mammals.

c. Frogs also obtain oxygen via diffusion across the skin.

d. Frog lung tissue has a greater density of capillary beds than mammalian lung tissue.

Compared with the interstitial fluid that bathes active muscle cells, blood reaching these cells in arterioles has a

a. Higher PO₂.

b. Higher PCO₂.

c. Greater bicarbonate concentration.

d. Lower pH.

Carp are fishes that thrive in stagnant-water habitats with low oxygen partial pressure. Compared with the hemoglobin of many other fish species, carp hemoglobin has an extremely high affinity for O₂.

Draw an oxygen–hemoglobin equilibrium curve showing separate lines for carp and a fish that lives in water with a higher oxygen partial pressure.

Explain why they differ.

What is the primary feedback used by the brain to control breathing?

a. Heart rate

b. Partial pressure of O₂

c. Blood pH, which indicates O₂ level

d. Blood pH, which indicates CO₂ level

During exercise, the cardiovascular system must supply muscles with large amounts of oxygen and fuel and get rid of a lot of waste.

How do the cardiovascular systems of athletes respond to prolonged exercise?

During athletic training, the oxygen–hemoglobin dissociation curve

a. Shifts to the right, unloading more oxygen to tissues.

b. Shifts to the right, unloading less oxygen to tissues.

c. Shifts to the left, unloading more oxygen to tissues.

d. Shifts to the left, unloading less oxygen to tissues.

Carbon monoxide (CO) is a colorless, odorless gas found in furnace and automobile engine exhaust and cigarette smoke. CO binds to hemoglobin 210 times more tightly than does O₂. CO also binds with an electron transport protein and disrupts cellular respiration. Explain why CO is such a deadly gas.

During exercise, the cardiovascular system must supply muscles with large amounts of oxygen and fuel and get rid of a lot of waste.

How do the cardiovascular systems of athletes respond to prolonged exercise?

When athletes exercise, what is the primary physiological variable responsible for their sustained increase in ventilation rate?

a. Decreased blood PO₂

b. Increased blood PCO₂

c. Increased blood pH

d. Increased body temperature

Partial pressure reflects the relative amount of gas in a mixture and is measured in millimeters of mercury (mm Hg). Llamas are native to the Andes Mountains in South America. The partial pressure of O₂ (abbreviated P_O₂) in the atmosphere where llamas live is about half of the P_O₂ at sea level. As a result, the PO₂ in the lungs of llamas is about 50 mm Hg, whereas that in human lungs at sea level is about 100 mm Hg. A dissociation curve for hemoglobin shows the percentage of saturation (the amount of O₂ bound to hemoglobin) at increasing values of P_O₂ As you see in the graph below, the dissociation curves for llama and human hemoglobin differ. Compare these two curves and explain how the hemoglobin of llamas is an adaptation to living where the air is 'thin.'