418 Chapter 17
(A)
Alveolus(B) 50 m(^) ®
Learning
Cengage ©
Wall of Wall of Red
alveolus capillary blood cell
(C) 1 m
(^) ®
Learning
Cengage ©
(^) ®
Learning
Cengage ©
Figure 17- 8 The anatomy of an alveolus.
contain over 300 million alveoli. This is an immense
surface area of 70 square meters (753 square feet) for the
exchange of oxygen and carbon dioxide. This is about the
square footage of a small house or cottage.
The Respiration Process.
The principal purpose of respiration is to supply the tril-
lions of cells of the body with oxygen and to remove the
carbon dioxide gas produced by cellular activities. There
are three basic processes of respiration. The first process
is ventilation or breathing, which is the movement of air
between the atmosphere and the lungs. Ventilation has two
phases: inhalation or inspiration to move air into the
lungs and exhalation or expiration to move air out of
the lungs (Figure 17 - 9).
The second and third processes of respiration in-volve
the exchange of the gases within the body. External
respiration is the exchange of gases between the lungs
and the blood, the second process. The third process is
called internal respiration, which is the exchange of
gases between the blood and the body cells.