Anatomy and physiology of the nasal cavity

The nose is composed of two nasal cavities, or spaces, separated by a middle wall, which is called the nasal septum. The nose warms, humidifies, and filters the air you inhale, protecting the delicate tissues within the lung.

On the outside walls of each nasal cavity is a series of three smooth ridges, called turbinates. The turbinates can alter the blood flow beneath their surface, thus increasing or decreasing their size, which in turn regulates the flow of air through the nose. In addition, the outer nasal cavity contains coarse hairs that trap large particles and prevent them from passing into the deeper part of the nasal cavity.

See an illustration of the nasal passage.

The sinuses, which are air-filled cavities behind the nose in the cheeks and forehead, have holes that drain into the nasal cavity either under or behind the middle turbinate. When these holes become blocked from inflammation of the nasal tissues or other causes, infection of the sinuses (sinusitis) can occur.

See an illustration of the nasal sinus cavities.

The passage that leads from the nasal airways to the upper portion of the throat (the pharynx) connects to the eustachian tube and the middle ear. When the eustachian tube is blocked, fluid can build up and cause otitis media (middle ear infection).

At the uppermost region of the nasal cavity is the olfactory mucosa. This specialized tissue is responsible for the sense of smell. Chemicals in the air stimulate special nerve endings in the olfactory mucosa. These nerve endings communicate with the brain, which interprets the signals and allows a person to identify a certain scent. When the uppermost part of the nasal cavity is swollen, such as from inflammation due to allergic rhinitis or a common cold, air cannot reach the olfactory mucosa and the person's sense of smell is reduced.

The entire nasal cavity is lined with a special lining called epithelium. The epithelium is composed of cells with cilia, tiny hairlike projections that move back and forth to remove particles from the nose. The epithelium is also composed of cells that produce mucus, which keeps the nasal tissues moist. Just below the epithelium are many nerves, arteries, and veins that allow for sensation and supply the tissues with oxygen and nutrients. In addition, the epithelium contains cells from the body's immune system. These cells are able to recognize foreign particles, such as cold viruses, so that the body can destroy them and avoid or minimize infection.