musculoskeletal action, which resembles that of abellows, causes air to be inhaled or exhaled.Physiological respiration involves an exchangeof gases, oxygen and carbon dioxide, at two points in thebody. The first is the transfer that occurs in the lungsbetween the incoming oxygen and the carbon dioxidepresent in the capillaries of the lungs (externalrespiration). The second transfer occurs when oxygenbrought into the body replaces carbon dioxide build upin the cellular tissue (internal respiration).Normally, oxygen and carbon dioxide exchange inequal volumes; however, certain physiologicalconditions may throw this balance off. For example,heavy smokers will find that the ability of their lungs toexchange gases is impaired, leading to shortness ofbreath and fatigue during even slight physical exertion.This debilitating situation is the direct result of theirinability to draw a sufficient amount of oxygen into thebody to replace the carbon dioxide build-up andsustain further muscular exertion. On the other hand,hyperventilation brings too much oxygen into thebody, overloading the system with oxygen, anddepleting the carbon dioxide needed for balance.ANATOMY OF THE RESPIRATORYSYSTEMAir enters the nasal chambers and the mouth, thenpasses through the pharynx, larynx, trachea, andbronchi into the bronchioles. Each bronchiole issurrounded by a cluster of alveoli (fig. 1-39).Nasal CavityAir enters the nasal cavity through the nostrils(nares). Lining the nasal passages are hairs, which,together with the mucous membrane, entrap and filterout dust and other minute particles that could irritatethe lungs. Incoming air is warmed and moistened in the1-33HM3f0138AREA DRAINED BYRIGHT LYMPHATICDUCTRIGHT LYMPHATICDUCTLEFT INTERNALJUGULAR VEINTHORACICDUCTLEFTSUBCLAVIANVEINTHORACICDUCTLYMPHATICTRUCKLYMPHNODELYMPHATICVESSELLEGENDFigure 1-38.—Pathway of right lymphatic duct and thoracic duct.
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