Paranasal Sinuses: Structure, Function & Diseases

The sinuses are air-filled cavities within the bony structure of the skull. The most common complaint is sinusitis, which is associated with pain and runny nose, but usually resolves after 10 days.

What are the sinuses?

The paranasal sinuses are spaces within the bony structure of the skull and face that are filled with air. These free cavities serve to heat and humidify the air we breathe, as well as act as a voice resonator. In addition, the paranasal sinuses reduce the weight of the skull, which would be much heavier without these cavities. The inner walls of the sinuses are covered with cells that secrete a moist secretion. This traps pathogens in the air we breathe before they enter the body and keeps the inside of the nose from drying out. The sinuses are divided into a total of four pairs. One pair behind the nostril, one above the eyes, one between the eyes, and one hollow chamber behind each of the ethmoid bones. Often referred to as just “sinuses,” however, the paranasal sinuses are just one type of sinus in the human body.

Anatomy and structure

Humans have four distinct pairs of paranasal sinuses: the maxillary sinus, the frontal sinus, the sphenoid sinus, and the ethmoid sinuses. The maxillary sinus is located below the eyes in the upper jaw bone. They are the largest sinuses and the first to develop in the growing organism. The frontal sinus is located in the frontal bone above the eyes. It forms after the second year of life and continues to grow into puberty. The sphenoid sinus forms in the center of the skull within the sphenoid bone and continues to grow into early adulthood. The ethmoid cells form several small air cells between the eyes. At birth, they are filled with fluid and continue to grow until 12 years of age. They are shaped like small pyramids and separated by thin septa.

Functions and tasks

The complete functions of the paranasal sinuses are still debated, but some tasks are suspected. They reduce the overall weight of the human head, especially the anterior region and facial bones. They improve the resonance of the voice. Paranasal sinuses can act as a kind of buffer in case of impacts against the face. The cavities insulate sensitive nerve pathways of the teeth or eyes from temperature changes in the incoming breath. They humidify and warm incoming air as airflow slows in these regions. The paranasal sinuses regulate the pressure balance of the intranasal region. They also serve an important function within the immune defense system by intercepting pathogens before they enter the respiratory tract. Apart from this conjecture about the function of the paranasal sinuses, it is equally possible that they do not serve any direct biological function. That is, they may equally be a spandrel (byproduct) of an actual biological adaptation that occurred during evolutionary development.

Diseases

The most common ailment that can occur in relation to the sinuses is sinusitis. It is caused by allergies, infections or other autoimmune disorders. In most cases, it results from a viral infection and subsides within 10 days. Sinusitis is defined as inflammation of the mucosal membranes covering the walls of the sinuses. The inflammation is divided into several degrees. Acute sinusitis is usually caused by a viral infection. If the cause is a bacterial infection, they are usually caused by pneumococcus or Haemophilus influenzae. While the viral pathogen lasts only 7-10 days, the bacterial infection is more persistent. People with diabetes or HIV are particularly susceptible to this type of infection, but chemical exposure, such as cigarette smoke, also increases susceptibility. Chronic sinusitis lasts longer than three months and can have a variety of different causes, which should be diagnosed individually after symptoms appear. Depending on which parts of the sinuses are affected by the inflammation, symptoms occur in different parts of the facial bones. Typical symptoms include pain, floppiness, and dizziness and/or pressure. Pain and pressure usually worsen with a change in body position, for example when the affected person lies down.Viral infections are cured, and antibiotics may be considered for bacterial infections.