753
CHAPTER NINETEEN
Respiratory System
Lung volume in milliliters (mL)
6,000
5,000
4,000
3,000
2,000
1,000
0
Total lung
capacity
Inspiratory
capacity
Functional
residual
capacity
Expiratory
reserve volume
Residual
volume
Tidal
volume
Vital
capacity
Inspiratory
reserve volume
volume of air that remains in the lungs following a resting
expiration.
The vital capacity plus the residual volume equals the
total lung capacity
(about 5,800 mL) (see F
g. 19.26). This
total varies with age, sex, and body size.
Some of the air that enters the respiratory tract during
breathing fails to reach the alveoli. This volume (about 150 mL)
remains in the passageways of the trachea, bronchi, and bron-
chioles. Gases are not exchanged through the walls of these
passages, so this air is said to occupy
anatomic dead space.
Occasionally, alveoli in some regions of the lungs are
nonfunctional due to poor blood fl
ow in the adjacent capil-
laries. This creates
alveolar dead space.
The anatomic and
alveolar dead space volumes combined equal
physiologic
dead space.
In a normal lung, the anatomic and physiologic
dead spaces are essentially the same (about 150 mL).
A spirometer
(f g. 19.27)
is used to measure respiratory
air volumes (except the residual volume) to evaluate the
course of respiratory illnesses, such as emphysema, pneu-
monia, lung cancer, and bronchial asthma.
Table 19.4
sum-
marizes respiratory air volumes and capacities.
PRACTICE
23
What is tidal volume?
24
Distinguish between inspiratory and expiratory reserve volumes.
25
How is vital capacity measured?
26
How is the total lung capacity calculated?
FIGURE 19.25
±Expiration.±(
a
) Normal resting expiration is due to elastic recoil of the lung tissues and the abdominal organs. (
b
) Contraction of the
abdominal wall muscles and posterior internal intercostal muscles aids maximal expiration.
FIGURE 19.26
Respiratory volumes and capacities.
Diaphragm
Abdominal organs
recoil and press
diaphragm upward
Abdominal wall
muscles contract
and compress
abdominal organs
Abdominal organs
force diaphragm
higher
Diaphragm
Posterior internal
intercostal muscles
pull ribs down and
inward
(a)
(b)
the volumes. If the inspiratory reserve volume (3,000 mL) is
combined with the tidal volume (500 mL) and the expiratory
reserve volume (1,100 mL), the total is termed the
vital capac-
ity
(4,600 mL). This capacity is the maximum volume of air a
person can exhale after taking the deepest breath possible.
The tidal volume (500 mL) plus the inspiratory reserve
volume (3,000 mL) gives the
inspiratory capacity
(3,500 mL),
which is the maximum volume of air a person can inhale fol-
lowing a resting expiration. Similarly, the expiratory reserve
volume (1,100 mL) plus the residual volume (1,200 mL) equals
the
functional residual capacity
(2,300 mL), which is the
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