Chapter 18 review questions

Question 1

Level Two reviewing concept
Concept map: Construct a map of gas transport using the following terms. You may add other terms.
alveoli
arterial blood
carbaminohemoglobin
carbonic anhydrase
chloride shift
dissolved CO2
dissolved O2
hemoglobin
hemoglobin saturation
oxyhemoglobin
PCO2
plasma
PO2
pressure gradient
red blood cell
venous blood

Answer 1

Start with Fig. 18.10.

Question 2

In respiratory physiology, it is customary to talk of the PO2 of the plasma. Why is this not the most accurate way to describe the oxygen content of blood?

Answer 2

Most oxygen is bound to hemoglobin, not dissolved in the plasma.

Question 3

Compare and contrast the following pairs of concepts:
a. transport of O2 and CO2 in arterial blood
b. partial pressure and concentration of a gas dissolved in a liquid

Answer 3

(a) Most O2 is transported bound to hemoglobin, but most CO2 is converted to HCO3-
(b) Concentration is the amount of gas per volume of solution, measured in units such as moles/L. Partial pressure and concentration are proportional, but concentration is affected by the gas solubility and therefore is not the same as partial pressure.

Question 4

Does HbO2 binding increase, decrease, or not change with decreased pH?

Answer 4

decrease

Question 5

Define hypoxia, COPD, and hypercapnia.

Answer 5

Hypoxia—low oxygen inside cells. COPD—chronic obstructive pulmonary disease (includes chronic bronchitis and emphysema). Hypercapnia—elevated CO2

Question 6

Why did oxygen-transporting molecules evolve in animals?

Answer 6

Oxygen is not very soluble in water, and the metabolic requirement for oxygen in most multicellular animals would not be met without an oxygen-transport molecule.

Question 7

Draw and label the following graphs:
a. the effect of ventilation on arterial PO2
b. the effect of arterial PCO2 on ventilation

Question 8

As the PO2 of plasma increases:
a. what happens to the amount of oxygen that dissolves in plasma?
b. what happens to the amount of oxygen that binds to hemoglobin?

Answer 8

(a) increases (b) increases

Question 9

If a person is anemic and has a lower-than-normal level of hemoglobin in her red blood cells, what is her arterial PO2 compared to normal?

Answer 9

Normal, because PO2 depends on the
PO2 of the alveoli, not on how much Hb is available for oxygen transport.

Question 10

Create reflex pathways (stimulus, receptor, afferent path, and so on) for the chemical control of ventilation, starting with the following stimuli:
a. increased arterial PCO2

b. arterial PO2 = 55 mm Hg

Be as specific as possible regarding anatomical locations. Where known, include neurotransmitters and their receptors.

Answer 10

(a) See Fig. 18.17. (b) See Fig. 18.13.

Question 11

Level Three problem solving:
Marco tries to hide at the bottom of a swimming hole by breathing in and out through 2 feet of garden hose, which greatly increases his anatomic dead space. What happens to the following parameters in his arterial blood, and why?
a. PCO2
b. PO2
c. bicarbonate ion
d. pH

Answer 11

Increased dead space decreases alveolar ventilation. (a) increases, (b) decreases, (c) increases, (d) decreases

Question 12

Which person carries more oxygen in his blood?
a. one with Hb of 15 g/dL and arterial PO2 of 80 mm Hg
b. one with Hb of 12 g/dL and arterial PO2 of 100 mm Hg

Answer 12

Person (a) has slightly reduced dissolved O2
but at PO2 = 80 Hb saturation is still about 95%. Most oxygen is transported on Hb but the increased
PO2 of 100 mm Hg cannot compensate for the decreased hemoglobin content.

Question 13

What would happen to each of the following parameters in a person suffering from pulmonary edema?
a. arterial PO2
b. arterial hemoglobin saturation
c. alveolar ventilation

Answer 13

(a) decrease, (b) decrease, (c) decrease

Question 14

In early research on the control of rhythmic breathing, scientists made the following observations. What hypotheses might the researchers have formulated from each observation?
a. Observation. If the brain stem is severed below the medulla, all respiratory movement ceases.
b. Observation. If the brain stem is severed above the level of the pons, ventilation is normal.
c. Observation. If the medulla is completely separated from the pons and higher brain centers, ventilation becomes irregular but a pattern of inspiration/expiration remains.

Answer 14

(a) Respiratory movements originate above the level of the cut, which could include any area of the brain. (b) Ventilation depends upon signals from the medulla and/or pons. (c) Respiratory rhythm is controlled by the medulla alone, but other important aspects of respiration depend upon signals originating in the pons or higher.

Question 15

A hospitalized patient with severe chronic obstructive lung disease has a PCO2 of 55 mm Hg and a PO2 of 50 mm Hg. To elevate his blood oxygen, he is given pure oxygen through a nasal tube. The patient immediately stops breathing. Explain why this might occur.

Answer 15

With chronic elevated PCO2, the chemoreceptor response adapts, and CO2 is no longer a chemical drive for ventilation. The primary chemical signal for ventilation becomes low oxygen (below 60 mm Hg). Thus, when the patient is given O2, there is no chemical drive for ventilation, and the patient stops breathing.

Question 16

You are a physiologist on a space flight to a distant planet. You find intelligent humanoid creatures inhabiting the planet, and they willingly submit to your tests. Some of the data you have collected are described below.

The graph above shows the oxygen saturation curve for the oxygen-carrying molecule in the blood of the humanoid named Bzork. Bzork’s normal alveolar
PO2 is 85 mm Hg. His normal cell PO2 is 20 mm Hg, but it drops to 10 mm Hg with exercise.

a. What is the percent saturation for Bzork’s oxygen-carrying molecule in blood at the alveoli? In blood at an exercising cell?

b. Based on the graph, what conclusions can you draw about Bzork’s oxygen requirements during normal activity and during exercise?

Answer 16

(a) Alveoli—96%; exercising cell—23%

(b) At rest, Bzork only uses about 20% of the oxygen that his hemoglobin can carry. With exercise, his hemoglobin releases more than 3/4 of the oxygen it can carry.

Question 17

The next experiment on Bzork involves his ventilatory response to different conditions. The data from that experiment are graphed below. Interpret the results of experiments A and C.

Answer 17

All three lines show that as PCO2 increases, ventilation increases. Line A shows that a decrease in PCO2 enhances this increase in ventilation (when compared to line B). Line C shows that ingestion of alcohol lessens the effect of increasing PCO2 on ventilation. Because alcohol is a CNS-depressant, we can hypothesize that the pathway that links increased PCO2 and increased ventilation is integrated in the CNS.

Question 18

The alveolar epithelium is an absorptive epithelium and is able to transport ions from the fluid lining of alveoli into the interstitial space, creating an osmotic gradient for water to follow. Draw an alveolar epithelium and label apical and basolateral surfaces, the airspace, and interstitial fluid. Arrange the following proteins on the cell membrane so that the epithelium absorbs sodium and water: aquaporins, Na+ -K+ ATPase, and epithelial Na+ channel (ENaC). (Remember: Na+ concentrations are higher in the ECF than in the ICF.)

Answer 18

Apical—faces airspace; basolateral—faces interstitial fluid. Apical side has ENaC and aquaporins; basolateral side has aquaporins and Na+ -K+ -ATPase. Na+ enters the cell through ENaC, then is pumped out the basolateral side. (Cl- follows to maintain electrical neutrality.) The translocation of NaCl allows water to follow by osmosis.