The nose is one of the least understood organs in the body. Its functions are respiration (breathing), humidification (warming) of inhaled air and smell. It is divided into the external nose, the nasal cavity and the paranasal sinuses, the three comprising what ENT surgeons call the sinonasal system. At the back of this system is the postnasal space (also called the nasopharynx), which connects the nasal cavity to the throat below.

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External nose

The external nose permits the passage of air into the nasal cavity via the nostrils. Protecting the nostrils are the vibrissae (nasal hairs) that serve to trap foreign particles and prevent them from getting inhaled. Due to its projection from the face, the external nose may be subject to injury and subsequent deformity.

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Nasal cavity

The nasal cavity is larger than most people realise and extends from the nostril right to the back of the nose (the postnasal space or nasopharynx), up to the cribiform plate (part of the floor of the skull upon which the brain sits) and down to the palate (roof of the mouth). It contains the three scroll-like turbinates (inferior, middle and superior; also called concha), which serve to humidify inhaled air. They do so by releasing heat from the well-vascularised lining of mucosa that covers them and moisture from the mucus that the mucosa naturally produces. The air, now warmed and moistened air, is easier to breathe. 

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The nasal cavity is divided into two halves by a partition called the nasal septum, which is made of cartilage in its front two-thirds and bone in its back third. The septum, together with the turbinates, serves to streamline inhaled air effeciently to the back of the nose and down into the lungs. 

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The lacrimal (tear) gland drains into the nasal cavity via the nasolacrimal duct. It drains behind the inferior (lowermost) turbinate. This is why your nose runs when you cry.

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Problems that may occur in the nasal cavity include the following (click on one for more information):

 - Deviated nasal septum (a bend in the nasal partition causing blockage)

 - Septal perforation (a hole in the nasal partition causing an abnormal communication between the two sides)

 - Rhinitis (chronic swelling of the nasal lining, or mucosa)

 - Nasal polyps (benign nasal swellings arising from an inflamed nasal lining)

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Paranasal sinuses

The nasal cavity opens into four main sinuses on either side:

1. Maxillary sinuses - located behind the cheeks, under the eyes

2. Ethmoid sinuses - a honeycombed system of sinuses located between the nose and the eye

3. Frontal sinuses - located in the forehead

4. Sphenoid sinuses - located behind the nose roughly in the centre of the head (see top diagram)

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Problems that may occur in the paranasal sinuses include the following (click for more information):

 - Sinusitis (acute or chronic infection of the paranasal sinuses)

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Postnasal space

At the very back of the nose is an area called the postnasal space. In the strictest sense it is not actually part of the nose, but rather the uppermost part of the pharynx (throat), known as the nasopharynx, which connects the nose to the lower parts of the throat. Within the postnasal space lie the adenoids and the openings of the Eustachian tubes. More about the adenoids can be read here. Enlargement of the adenoids in this area may cause problems, including:

 - Nasal obstruction causing mouth breathing

 - Sleep disturbances such as snoring and sleep apnoea

 - Glue ear

 - Acute otitis media (middle ear infections)

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