The term of sinus (a “channel” or “hollow space”) is defined as any cavity within a bone but is most often used to identify the muscus lined air cavities in the facial bones and certain blood passageways in animals. In humans, sinuses surround the nose and are known as the paranasal sinuses. They extend from the nasal cavities into adjoining bones and are connected to the nose by passageways. The panasal sinuses are thought to help warm and moisten inhaled air. They also reduce the weight of the skull and perhaps modify vocal sounds. The bones that contain sinuses are the frontal, sphenoid, ethmoid, and maxillary bones.

The paranasal sinuses are lined with a mucosa, or moist membrane. Glands are present within the mucosa, and ciliated and gobiet cells occurs on the surface, exposed to the air space in the sinus. The ciliated cells exhibit hairlike processes that beat back and forth. They serve to keep the air that enters the lungs clean by trapping dust and dirt. The particles and mucus eventually reach the pharynx and are swallowed. An inflammation of the mucosa is called sinusitis.

Sinuses in blood passageways include the capillary spaces of the liver; spaces in the common carotid artery and the aorta; and maternal sinusoids, which are small channels in the wall of the uterus of a pregnant woman.


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