BIO 360 - Exam 4 - Chapter 18 Review Questions

Question 1

List five factors that influence the diffusion of gases between alveolus and blood.

Answer 1

Pressure gradients, solubility in water, alveolar capillary perfusion, blood pH, temperature.

Question 2

More than     % of the oxygen in arterial blood is transported bound to hemoglobin. How is the remaining oxygen transported to the cells?

Answer 2

98%. Remainder is dissolved in plasma.

Question 3

Name four factors that influence the amount of oxygen that binds to hemoglobin. Which of these four factors is the most important?

Answer 3

PO2, temperature, pH, and the amount of hemoglobin available for binding (most important).

Question 4

Describe the structure of a hemoglobin molecule. What chemical element is essential for hemoglobin synthesis?

Answer 4

Four globular protein chains, each wrapped around a central heme group. Requires iron.

Question 5

The networks for control of ventilation are found in the      and      of the brain. What do the dorsal and ventral respiratory groups of neurons control? What is a central pattern generator?

Answer 5

medulla and pons. Dorsal—neurons for inspiration; ventral—neurons for inspiration and active expiration. Central pattern generator—group of neurons that interact spontaneously to control rhythmic contraction of certain muscle groups.

Question 6

Describe the chemoreceptors that influence ventilation. What chemical is the most important controller of ventilation?

Answer 6

Medullary chemoreceptors increase ventilation when PCO2 increases. Carotid body chemoreceptors respond to PCO2, pH, and PO2<60 mm Hg. PCO2 is most important.

Question 7

Describe the protective reflexes of the respiratory system.

Answer 7

They include irritant-mediated bronchoconstriction and the cough reflex.

Question 8

What causes the exchange of oxygen and carbon dioxide between alveoli and blood or between blood and cells?

Answer 8

Partial pressure gradients

Question 9

List five possible physical changes that could result in less oxygen reaching the arterial blood.

Answer 9

Decreased atmospheric PO2, decreased alveolar perfusion, loss of hemoglobin, increased thickness of respiratory membrane, decreased respiratory surface area, increased diffusion distance.

Question 10

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 10

Start with Fig. 18.10.

Question 11

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 11

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

Question 12

Compare and contrast the following pairs of concepts:
(a) transport of O2 and PO2 in arterial blood
(b) partial pressure and concentration of a gas dissolved in a liquid

Answer 12

(a) Most O2 is transported bound to hemoglobin, but most CO2 is converted to HCO −3. (b) Concentration is 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 13

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

Answer 13

decrease

Question 14

Define hypoxia, COPD, and hypercapnia.

Answer 14

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

Question 15

Why did oxygen-transporting molecules evolve in animals?

Answer 15

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 16

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

Answer 16

(a) x-axis—ventilation in L/min; y-axis—arterial pO2, in mm Hg. See Fig. 18.9. (b) x-axis—arterial pCO2 in mm Hg; y-axis—ventilation in L/min. As arterial pCO2 increases, ventilation increases. There is a maximum ventilation rate, and the slope of the curve decreases as it approaches this maximum.

Question 17

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 17

(a) increases (b) increases

Question 18

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 18

Normal, because pO2 depends on the pO2 of the alveoli, not on how much Hb is available for oxygen transport.

Question 19

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 = 55mmHg

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

Answer 19

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

Question 20

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 20

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

Question 21

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 21

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 22

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 22

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

Question 23

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 23

(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 24

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 24

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 25

x

Question 26

x

Question 27

x

Question 28

x

Question 29

x

Question 30

Describe what happens to the oxygen-hemoglobin saturation curve in Figure 18.9a when blood hemoglobin falls from 15 g/dL blood to 10 g/dL blood.

Answer 30

Nothing. The percent saturation of Hb is unchanged at any given PO2. However, with less Hb available, less oxygen will be transported.