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Structure and Function

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.

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.

image Learning Style Tip

Go to the campus library or get permission to spend some time in the anatomy and physiology or biology laboratory at your school. Study the anatomical models, in this case the ones representing the respiratory system. Physically touch the various parts, naming them as you do, while you also name their associated combining forms. Make a video of yourself as you do this so you can study the models again from home. Share your videos with your classmates!


Aspiration is a term that is often used to describe food or fluids being sucked into the lungs.

As 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 as 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 as it drains into the nasal cavities.

Air moves to the lower airway as it flows past the epiglottis and enters the trachea. The epiglottis acts as a doorway to the trachea and serves a vital protective function by opening to let in air and closing to keep out food and fluid. The trachea is approximately 5 inches long and gets its shape and strength from numerous rings of cartilage. It separates the upper and lower airways. As air flows through the tracheal entrance, it passes through the larynx. This structure vibrates to create sound when we talk. Air then flows down ...

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