Ganong's Review of Medical Physiology, 23rd Edition

CHAPTER 35

Pulmonary Function 591

veins (Figure 35–4). The separate and much smaller bronchial
circulation includes the bronchial arteries that come from sys-
temic arteries. They form capillaries, which drain into bron-
chial veins or anastomose with pulmonary capillaries or veins
(Figure 35–5). The bronchial veins drain into the azygos vein.
The bronchial circulation nourishes the trachea down to the
terminal bronchioles and also supplies the pleura and hilar
lymph nodes. It should be noted that lymphatic channels are
more abundant in the lungs than in any other organ.

MECHANICS OF RESPIRATION

INSPIRATION & EXPIRATION

The lungs and the chest wall are elastic structures. Normally,

no more than a thin layer of fluid is present between the lungs

and the chest wall (intrapleural space). The lungs slide easily

on the chest wall, but resist being pulled away from it in the

same way that two moist pieces of glass slide on each other but

resist separation. The pressure in the “space” between the

lungs and chest wall (intrapleural pressure) is subatmospheric

(Figure 35–6). The lungs are stretched when they expand at

birth, and at the end of quiet expiration their tendency to re-

coil from the chest wall is just balanced by the tendency of the

FIGURE 35–3
Portion of an interalveolar septum in the adult human lung. A)
A cross-section of the respiratory zone shows the relation-
ship between capillaries and the airway epithelium. Only 4 of the 18 alveoli are labeled.
B)
Enlargement of the boxed area from (A) displaying in-
timate relationship between capillaries, the interstitium, and the alveolar epithelium.
C)
Electron micrograph displaying area depicted in (B). The
pulmonary capillary (cap) in the septum contains plasma with red blood cells apposed to the thin epithelial cells that line the alveoli. Note the
closely apposed endothelial wall and pulmonary epithelium, separated at places by connective tissue fibers (cf); en, nucleus of endothelial cell;
epl, nucleus of type I alveolar epithelial cell; a, alveolar space; ma, alveolar macrophage.
(Reproduced with permission from (A, B) Widmaier EP, Raff H, Strang
KT:
Vander’s Human Physiology: The Mechanisms of Body Function
, 11th ed. McGraw-Hill, 2008; and (C) Burri PA: Development and growth of the human lung. In:
Handbook of
Physiology,
Section 3,
The Respiratory System.
Fishman AP, Fisher AB [editors]. American Physiological Society, 1985.)

Respiratory

bronchiole

Alveolar duct

Alveolus

Alveolus pore

Alveolus

Alveolus

Capillaries

Capillary

endothelium

Alveolar air Type II cell

Type I cell Alveolar air

Interstitium

Plasma

in capillary

Basement

membrane

B

A

Erythrocyte

Erythrocyte

a

ma

a

cf

cf

cap

epI

en

C