The sinus cavities, also known as the paranasal sinuses, are hollows in the bones of the face which are designed to serve a number of important functions. Humans and many other animals including birds have sinuses. These cavities are only visible on X-rays, and in fact these cavities are unique, and they have been used like fingerprints in forensic examinations. The term “sinus” is actually Latin for “cavity,” making “sinus cavities” a rather redundant term, although many people are unaware of this.
There are four sets of sinuses in the skull. The ethmoid sinuses are located between the eyes, while the sphenoid sinuses are behind the eyes. In the upper jaw, underneath the eyes, one can find the maxillary sinuses, and the frontal sinuses are above the nose. Each cavity is lined with a mucus membrane and numerous cilia, tiny hairs which move, forcing the contents of the sinuses to move through the cavity and drain through the nose.
One of the key functions of the sinus cavities is to drain mucus. Mucus is used to trap harmful substances which could otherwise penetrate the body, and it is generated by the body all the time. The sinuses facilitate collection and drainage of mucus so that it cannot accumulate and cause the development of an infection. This reduces the risk of infection for the body as bacteria and viruses are caught in the mucus, and it can also trap potential allergens as well.
These cavities also filter and warm the air inhaled by the body, and they act to lighten the skull. If the sinus cavities were filled in with bone, the skull would be extremely heavy and dense, which would make it hard to move. The sinuses also add resonance to the voice, and help to protect the skull in the event of an impact to the face.
Sinuses can develop problems. The most common problem occurs when they become filled with mucus and are unable to drain, leading to sinusitis, in which an inflammation of the sinus cavities occurs. The failure to drain may cause pain, and it leaves people with a feeling of heaviness and fatigue. Chronic sinusitis can be extremely irritating, and in some cases a surgical technique may be used to enlarge the sinuses and their drainage outlets to reduce the buildup of mucus and fluid. Cancers can also develop in the sinuses, with the potential to metastasize to other areas of the body.