Chapter 22
The Respiratory System
813
22
Capillary
Elastic
fibers
(a) Diagrammatic view of capillary-alveoli relationships
(b) Scanning electron micrograph of pulmonary capillary
casts (70x)
Smooth
muscle
Alveolus
Capillaries
Terminal bronchiole
Respiratory
bronchiole
Type II
alveolar cell
Type I
alveolar cell
Endothelial cell nucleus
Macrophage
Alveoli (gas-filled
air spaces)
Red blood cell
in capillary
Alveolar pores
Capillary endothelium
Fused basement membranes
of alveolar epithelium and
capillary endothelium
Alveolar epithelium
Respiratory
membrane
Red blood cell
O
2
Alveolus
CO
2
Capillary
Alveolus
Nucleus of type I
alveolar cell
(c) Detailed anatomy of the respiratory membrane
Figure 22.9
Alveoli and the respiratory membrane.
Elastic fibers and capillaries surround
all alveoli, but for clarity they are shown only on some alveoli in (a). In (b), the tissue forming the
alveoli has been removed. Only the capillary network remains.
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