LEARNING OBJECTIVE: Identify the location and function of each part of the respiratory system, and recall the process of respiration.

Respiration is the exchange of oxygen and carbon dioxide between the atmosphere and the cells of the body. There are two phases of respiration:

Physical, ormechanical, respiration involves the motion of the diaphragm and rib cage. The

Figure 1-37.-Lymphatic capillary and vessel.

musculoskeletal action, which resembles that of a bellows, causes air to be inhaled or exhaled.

Physiological respiration involves an exchange of gases, oxygen and carbon dioxide, at two points in the body. The first is the transfer that occurs in the lungs between the incoming oxygen and the carbon dioxide present in the capillaries of the lungs (external respiration). The second transfer occurs when oxygen brought into the body replaces carbon dioxide build up in the cellular tissue (internal respiration).

Normally, oxygen and carbon dioxide exchange in equal volumes; however, certain physiological conditions may throw this balance off. For example, heavy smokers will find that the ability of their lungs to exchange gases is impaired, leading to shortness of breath and fatigue during even slight physical exertion. This debilitating situation is the direct result of their inability to draw a sufficient amount of oxygen into the body to replace the carbon dioxide build-up and sustain further muscular exertion. On the other hand, hyperventilation brings too much oxygen into the body, overloading the system with oxygen, and depleting the carbon dioxide needed for balance.