ANATOMY OF THE RESPIRATORY SYSTEM

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. ANATOMY OF THE RESPIRATORY SYSTEM Air enters the nasal chambers and the mouth, then passes through the pharynx, larynx, trachea, and bronchi into the bronchioles. Each bronchiole is surrounded by a cluster of alveoli (fig. 1-39). Nasal Cavity Air enters the nasal cavity through the nostrils (nares). Lining the nasal passages are hairs, which, together with the mucous membrane, entrap and filter out dust and other minute particles that could irritate the lungs. Incoming air is warmed and moistened in the 1-33 HM3f0138 AREA DRAINED BY RIGHT LYMPHATIC DUCT RIGHT LYMPHATIC DUCT LEFT INTERNAL JUGULAR VEIN THORACIC DUCT LEFT SUBCLAVIAN VEIN THORACIC DUCT LYMPHATIC TRUCK LYMPH NODE LYMPHATIC VESSEL LEGEND Figure 1-38.—Pathway of right lymphatic duct and thoracic duct.