VPB 121: Veterinary Physiology - II (2+1)

EXTERNAL AND INTERNAL RESPIRATION

• External respiration, also called pulmonary gas exchange, is the diffusion of O₂ and CO₂ from the alveoli to pulmonary blood. Blood circulating through the body picks up CO₂ and delivers O₂. As this blood travels through the pulmo­nary capillaries, CO₂ diffuses into the alveoli while O₂ diffuses from the alveoli to pulmonary blood. The exchange of these gases occurs independently and passively.
• Pulmonary gas exchange is facilitated by a very thin respiratory membrane.
• Ventilation is generally regarded as the process by which gas in closed places is renewed or exchanged. As it applies to the lungs, it is a process of exchanging the gas in the airways and alveoli with gas from the envi­ronment. The main function of breathing is to provide gas for ventilation.
• In addition, there is a close association between the amount of gas reaching the alveoli (ventilation), and the blood flow through the pulmonary capillaries (perfusion).
• Internal respiration, or systemic gas exchange, occurs at the tissue level, where there is an exchange of O₂ and CO₂ between systemic capillaries and tissue. O₂ diffuses from the capillaries into the cells; CO₂ diffuses from the cells into the systemic capillaries.