Human Physiology, 14th edition (2016)

Respiratory Physiology 537

of the lungs, including their compliance, elasticity, and sur-

face tension.

Figure 16.8 Radiographic (x-ray) views of the

chest. These are x-rays ( a ) of a normal female and ( b ) of a

normal male.

(a)

(b)

Figure 16.7 A cross

section of the thoracic

cavity. In addition to the lungs,

the mediastinum and pleural

membranes are visible. The parietal

pleura is shown in green, and the

visceral pleura in blue.

Sternum Pericardial

Anterior cavity

mediastinum

Thoracic wall

Lung

Parietal

pericardium

Visceral

pericardium

Esophagus

Posterior mediastinum

Thoracic vertebra

Bronchus

Pleural cavity

Visceral pleura

Parietal pleura

Heart (in middle

mediastinum)

LEARNING OUTCOMES

After studying this section, you should be able to:

3. Explain how intrapleural and intrapulmonary
   pressures change during breathing.


4. Explain how lung compliance, elasticity, and surface
   tension affect breathing, and the significance of
   pulmonary surfactant.

Movement of air from higher to lower pressure, between the

conducting zone and the terminal bronchioles, occurs as a

result of the pressure difference between the two ends of the

airways. Air flow through bronchioles, like blood flow through

blood vessels, is directly proportional to the pressure differ-

ence and inversely proportional to the frictional resistance to

flow. The pressure differences in the pulmonary system are

induced by changes in lung volumes. The compliance, elastic-

ity, and surface tension of the lungs are physical properties that

affect their functioning.

Intrapulmonary and

Intrapleural Pressures

The visceral and parietal pleurae are stuck to each other like

two wet pieces of glass. The intrapleural space between them