The Functions of Internal & External Nares

Animals and human beings have sensitive noses.
Animals and human beings have sensitive noses. (Image: Brand X Pictures/Brand X Pictures/Getty Images)

Your nose may not be the most beautiful feature on your face, but it's one of the most sensitive. Without your nose, your lungs might fill up with debris; the shock of cold, dry air might affect your breathing; and the continuous loss of moisture during expiration might deplete your bodily-fluid levels.

Basic Anatomy

The nose is divided down the midline into two channels by a septum, or wall of cartilage. The external nares, or nostrils, are the openings you see at the base of the nose, inside of which are thicker hairs that act as filters. Farther inside the nose, in the internal nares, mucous membrane also known as mucosa, lines the two channels and the internal structures of the nose including the superior, middle and inferior conchae on each side of the septum. These are long, furled shells of bone that contribute to temperature and water control.

Filtering Air

The first line of defense against insects, dust and debris in the air is the layer of hairs that line the inside of each side of the external nares. Sensory nerves within the mucosa stimulate a sneeze or a mucous response to expel the debris before it reaches farther into the nose. The cilia of the internal nares are smaller and finer, and waft mucus that carries dust and other particles to the opening above the esophagus, or food tube, so that it can be swallowed and not passed into the trachea.

Warming Air

Each side of the nares is well supplied with blood in the form of capillaries, the smallest of blood vessels that carry blood and heat to the most peripheral parts of the body. These capillaries lie within the mucosal layer, and as air passes through the nares, heat is transferred from the capillaries to the air. Warming the air protects the lungs from temperature shock and helps to maintain core temperature.

Moistening and Dehumidifying Air

The lungs must remain moist in order to function, and the body's water balance must remain within normal ranges. When air passes through the conchae on its way to the lungs during inspiration, it picks up moisture so as to protect the lining of the lungs. When air is expired and reaches the nose, it passes back through the conchae where moisture from the expired air is deposited as fine condensate.

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