cal that improves the flexibility of the lung tissue, allowing
the lungs to expand more easily. In addition, macrophages
remove dust and debris from the alveolar space.
The Respiratory System Performs
Two Important Processes:
Breathing and Respiration
In order to have gas exchange, the alveoli must be filled
with fresh air. Several processes must occur to get ad-
equate amounts of oxygen from the air to the body cells
and to get carbon dioxide waste products from the body
cells back into the air:
Breathing
(pulm onary v e n tila tio n ).
Flow of air into and
out of the lungs.
Respiration. Exchange of gases across membranes:
• External respiration is gas exchange between the
alveoli and the blood in pulmonary capillaries—an
exchange with the “external” environment. Here,
the blood picks up oxygen from the air and releases
carbon dioxide into the air.
• Internal respiration is gas exchange between the
tissue cells and the blood in the systemic capillaries—
an exchange with the “internal” environment of the
body. Here the blood releases oxygen into the tissues
and picks up carbon dioxide from them.
1.
Which
structures direct air from the upper re-
spiratory tract into the alveoli of the lungs?
2.
What
is the major function of the respiratory
system?
3.
What
is the difference between external and
internal respiration?
Diffusioi
of O2
b. Structure of
an
alveolus
Type II
alveolar
cell secretes surfactant
a phospholipid mixture that prevents the
alveolus from collapsing and makes the
lungs more stretchy.
Alveolus is an air-filled sac that is
the terminal part of the airways.
Interstitial space—Space
between cells filled with
interstitial fluid.
Alveolar cell—Thin-walled
squamous epithelial cell that
is the site of gas exchange.
Alveolar fluid containing surfactant
Alveolar macrophage—Phagocytes
that wander through the alveoli and
remove dust and debris from alveolar
spaces.
Red blood cell in
pulmonary capillary
Diffusio
of CO2
Alveolus j| .
.
\
Respiratory membrane
Red blood cell
Capillary endothelium
Capillary basement
membrane
Alveolar cell
basement membrane
Respiratory Organs Move Air and Exchange Gases
375
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