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Structure and Function
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The most basic human need is the need to breathe. We take our first breaths as soon as we are born and continue this vital function through the last moments of our lives. The complex and amazing structures of the respiratory system support this life-sustaining process.
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When studying the respiratory system, we often divide it into the upper and lower airways. The upper airway consists of the mouth, nose, sinuses, and pharynx. The pharynx is further divided into the nasopharynx (back of the nose) and oropharynx (back of the mouth). The nose begins with the nares (nostrils) and extends back to the nasopharynx. The nasal passages are divided into right and left sides by the nasal septum. The hard palate divides the nasal cavity from the mouth, which sits beneath it. The sinus cavities are air-filled spaces named for the facial bones within which they are located; they include the maxillary, frontal, ethmoidal, and sphenoidal sinuses. Refer to Figure 8-1, which illustrates these structures, as we discuss the path that air takes into and out of the body.
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Flashpoint
Aspiration is a term that is often used to describe food or fluids being sucked into the lungs.
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While air moves through the upper airway, it is warmed, filtered, and humidified. Mucous membranes that line these structures contribute moisture to humidify the air. Cilia (tiny hairs) within the nasal cavity help filter the air by removing debris. The rich blood supply of all of these structures warms the air while it passes through. Sinus cavities serve to decrease the weight of the skull, provide resonance for the voice, and produce mucus, which helps eliminate microorganisms while it drains into the ...