Air passes through a series of tubes before gas exchange takes place across a very extensive moist surface. 166
9.2 Mechanism of Breathing
Respiration comprises breathing, external and internal respiration, and cellular respiration. 170During inspiration, the pressure in the lungs decreases, and air comes rushing in. During expiration, increased pressure in the thoracic cavity causes air to leave the lungs. 172-73
9.3 Gas Exchanges in the Body
External respiration occurs in the lungs where oxygen diffuses into the blood and carbon dioxide diffuses out of the blood. 174Internal respiration occurs in the tissues where oxygen diffuses out of the blood and carbon dioxide diffuses into the blood. 174The respiratory pigment hemoglobin transports oxygen from the lungs to the tissues and aids in the transport of carbon dioxide from the tissues to the lungs. 174
9.4 Respiration and Health
The respiratory tract is especially subject to disease because it is exposed to infectious agents. 177Smoking tobacco contributes to three major lung disorders-chronic bronchitis, emphysema, and cancer. 179, 181
9.5 Homeostasis
The respiratory system works with the other systems of the body to maintain homeostasis. 184 s