the RespiRatoRy system 193Hemoglobin binds with or releases oxygen in response
to shifts in oxygen levels, carbon dioxide levels, pH, and
temperature.
Driven by its partial pressure gradient, carbon dioxide
diffuses from cells across tissue fluid and into the bloodstream.
Most CO 2 reacts with water to form bicarbonate; the reactions
are speeded by the enzyme carbonic anhydrase. They are
reversed in the lungs, where carbon dioxide diffuses from lung
capillaries into the air spaces of the alveoli, then is exhaled.
section 10.6 Gas exchange is regulated
by the nervous system and by chemical
controls in the lungs. A respiratory pacemaker
in the medulla (part of the brain stem) sets the
normal, automatic rhythm of breathing in and
out (ventilation).
The nervous system monitors the levels of oxygen and
carbon dioxide in arterial blood by way of sensory receptors.
These include carotid bodies (at branches of carotid arteries
leading to the brain), aortic bodies (in an arterial wall near the
heart), and receptors in the medulla of the brain. Blood levels
of carbon dioxide are most important in triggering nervous
system commands that adjust the rate and depth of breathing.
rEviEW QUEstions
- In the diagram below, label the parts of the respiratory
system and the structures that enclose some of its parts.
6. How does hemoglobin help maintain the oxygen partial
pressure gradient during gas transport in the body?
7. What reactions enhance the transport of carbon dioxide
throughout the body? How is carbon dioxide moved out of
the body?
8. How do nerve impulses from the brain regulate ventilation
of the lungs? How are the rate and depth of breathing
controlled?
9. Why does your breathing rate increase when you exercise?
What happens to your heart rate at the same time—and why?
sELf-QUiz Answers in Appendix VI
- A partial pressure gradient of oxygen exists between.
a. air and lungs
b. lungs and metabolically active tissues
c. air at sea level and air at high altitudes
d. all of the above - The is an airway that connects the nose and mouth
with the.
a. oral cavity; larynx
b. pharynx; trachea
c. trachea; pharynx
d. pharynx; larynx - Oxygen in air must diffuse across to enter the blood.
a. pleural sacs c. a moist respiratory surface
b. alveolar sacs d. both b and c - Each lung encloses a.
a. diaphragm c. pleural sac
b. bronchial tree d. both b and c - Gas exchange occurs at the.
a. two bronchi c. alveoli
b. pleural sacs d. both b and c - Breathing.
a. ventilates the lungs
b. draws air into airways
c. expels air from airways
d. causes reversals in pressure gradients
e. all of the above - After oxygen diffuses into lung capillaries, it also diffuses
into and binds with.
a. tissue fluid; red blood cells
b. tissue fluid; carbon dioxide
c. red blood cells; hemoglobin
d. red blood cells; carbon dioxide - Due to its partial pressure gradient, carbon dioxide diffuses
from cells into tissue fluid and into the ; in the
lungs, carbon dioxide diffuses into the.
a. alveoli; bronchioles
b. bloodstream; bronchioles
c. alveoli; bloodstream
d. bloodstream; alveoli - Hemoglobin performs which of the following respiratory
functions?
a. transports oxygen
b. transports some carbon dioxide
c. acts as a buffer to help maintain blood pH
d. all of the above
© Cengage Learning- What is the difference between respiration and aerobic
cellular respiration? - Explain what a partial pressure gradient is and how such
gradients figure in gas exchange. - What is oxyhemoglobin? Where does it form?
- What drives oxygen from the air spaces in alveoli, through
tissue fluid, and across capillary epithelium? What drives
carbon dioxide in the opposite direction?
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