The human body contains air-filled spaces known as sinuses, which are primarily located within the skull. These cavities are part of the respiratory system and play a role in how we interact with the air around us. While often unnoticed, they become apparent when issues like inflammation arise, leading to pressure and discomfort.
Sinus Locations and Types
The human skull houses four main pairs of paranasal sinuses, each named after its bone. These symmetrical cavities are located on each side of the face, contributing to the overall facial shape.
The frontal sinuses are located in the frontal bone, above the eyebrows. These triangular sinuses are the most superior and vary in size. They can extend into the orbital part of the frontal bone.
The maxillary sinuses are beneath the eyes, within the maxillary bone (upper jaw). These are the largest paranasal sinuses, positioned laterally to the nasal cavities. They are often a common site for sinus infections.
The ethmoid sinuses are a collection of small air cells within the ethmoid bone, located between the eyes, behind the bridge of the nose. Unlike other sinuses, they consist of multiple small cavities. These air cells are divided into anterior, middle, and posterior groups.
Deep within the skull, behind the eyes and upper nasal cavity, lie the sphenoid sinuses. These paired cavities are within the butterfly-shaped sphenoid bone, making them the deepest. Their size and shape can vary among individuals.
Internal Sinus Appearance
Internally, sinuses are lined with a specialized tissue called mucosa. This respiratory mucosa is a ciliated epithelium, composed of cells with tiny, hair-like projections called cilia.
Interspersed within this ciliated epithelium are goblet cells, which are responsible for producing mucus. This mucus forms a thin layer that coats the internal surfaces of the sinuses. In a healthy sinus, this mucus blanket is constantly moved by the coordinated beating of the cilia.
The cilia work to sweep the mucus and trapped particles towards the drainage openings of the sinuses, leading into the nasal cavity. This continuous flow helps to clear out dust, germs, and other foreign invaders. A healthy sinus cavity appears as an air-filled space with a moist, smooth mucosal lining.
Functions of the Sinuses
Sinuses serve several important roles. One function is to reduce the overall weight of the skull. Their air-filled nature makes the head lighter, easing the burden on neck muscles.
Sinuses also play a role in conditioning the air we breathe. They help to humidify and warm inhaled air before it reaches the lungs, making it healthier for the respiratory system. This process protects the more sensitive structures of the airways.
Sinuses influence voice resonance. As air vibrates within these hollow spaces, it contributes to the unique sound and quality of a person’s voice. They can also act as a protective “crumple zone” for the brain and eyes by absorbing impact during facial trauma.