choanen

Choanen are the internal openings of the nasal cavity into the pharynx. They are also known as the posterior nasal apertures. There are two choanae, one on each side of the internal nose. These openings are bordered anteriorly by the vomer, laterally by the pterygoid processes of the sphenoid bone, and superiorly by the body of the sphenoid bone. The soft palate forms the inferior border.

The choanae play a crucial role in the respiratory and olfactory systems. They allow air to pass from the nasal cavity to the pharynx, which is the first step in breathing. This pathway also allows for the warming, humidifying, and filtering of inhaled air before it reaches the lungs. Furthermore, the choanae are important for olfaction, as they direct airborne odor molecules from the nasal cavity towards the olfactory epithelium located in the roof of the nasal cavity. During swallowing, the soft palate elevates to close off the choanae, preventing food and liquid from entering the nasal cavity. Congenital choanal atresia, a condition where one or both choanae are blocked, can cause significant breathing difficulties, especially in newborns, as they are obligate nasal breathers.