The nasal cavity and paranasal sinuses
The nasal cavity and the paranasal sinuses are part of the body’s respiratory system.
Structure of the nasal cavity
The nose is the beginning of the respiratory tract. The nostrils are the 2 openings in the nose.
The nasal vestibule is the area just inside the nostril. It is supported by cartilage and lined with skin containing coarse hairs. These hairs help trap large particles such as sand, dust and even insects to prevent them from entering the nasal cavity.
The nasal vestibule opens into the nasal cavity. The nasal cavity is divided into left and right sides by a wall of cartilage and bone (called the nasal septum). The nasal cavity is above the roof of the mouth (called the palate) and surrounded by the paranasal sinuses. It joins with the nasopharynx, which is the upper part of the pharynx, or throat, at the back of the mouth.
Structure of the paranasal sinuses
Paranasal means around the nose. The paranasal sinuses are air filled cavities around the nose within the skull. The paranasal sinuses are connected to one another and to the nasal cavity.
Types of paranasal sinuses
There are 4 pairs of paranasal sinuses.
Maxillary sinuses are in the maxilla (the upper jaw) on each side of the nose, behind the cheeks and below the eyes. They are shaped like pyramids. They are the largest of the paranasal sinuses.
Frontal sinuses are in the frontal bone, above the nose and behind the eyebrows. They are 2 cavities divided by a thin wall of bone.
Ethmoid sinuses are small cavities in the ethmoid bone, above the nasal cavity and between the eyes. They can vary in number and size.
The sphenoid sinus is found in the sphenoid bone, which is deep in the skull. It is behind the ethmoid sinuses and nasal cavity. It is separated into a left and right sinus by an incomplete, thin wall of bone.
Types of cells in the nasal cavity and paranasal sinuses
Several types of cells make up the lining of the nasal vestibule, nasal cavity and paranasal sinuses.
As you go farther into the nasal vestibule and into the nasal cavity, the cells change from flat squamous cellssquamous cellsA type of epithelial cell that is thin, flat and looks like a fish scale. to taller cells shaped like columns. On the surface of the column-shaped cells in the nasal cavity and paranasal sinuses are hair-like structures called cilia. The cilia beat to help move mucus toward the back of the throat, where it can be swallowed.
The nasal cavity and paranasal sinuses have other types of cells that make mucus. As the mucus moves through the nasal cavity and sinuses, it moisturizes and cleans the surface and traps bacteria, dust and other particles from the air breathed through the nose. The mucus drains into the throat and is swallowed, where the acid in the stomach destroys any bacteria that were in the mucus.
The upper part of the nasal cavity has specialized nerve fibres (called olfactory nerve fibres) that provide a sense of smell.
Other structures of the head and neck
Lymph nodes, cranial nerves and the skull are other important structures in the head and neck.
There are large numbers of lymph nodes in the neck (called cervical lymph nodes). These lymph nodes are grouped by their location in the neck. Nasal cavity and paranasal sinus cancers can spread to cervical lymph nodes. A neck dissection may be done to remove lymph nodes that have cancer in them or to prevent cancer from spreading to them. Find out more about cervical lymph nodes and neck dissection.
Nasal cavity and paranasal sinus cancer can spread to other lymph nodes in the head and neck, but this happens less often than spread to the cervical lymph nodes.
The cranial nerves control many functions in the head and neck, such as swallowing, vision, smell, hearing and eye movement. Some cranial nerves run close to the nasal cavity and paranasal sinuses. Sometimes a tumour in the nasal cavity or paranasal sinus can spread to the cranial nerves. If the cranial nerves are in the treatment area, your healthcare team will try to protect these nerves as much as possible. Sometimes nasal and paranasal cancer or treatments can damage the cranial nerves, which can lead to temporary or permanent problems. There are 12 pairs of cranial nerves.
Find out more about cranial nerves.
Bones of the skull
The skull is made up of 22 bones. The cranium is the part of the skull that surrounds and protects the brain. The front part of the skull is made up of the bones of the face (facial bones). The facial bones protect and support the entrances to the respiratory and digestive systems.
The nasal cavity and the paranasal sinuses are within the skull. Nasal cavity and paranasal sinus cancer can spread to the bones of the skull, such as the orbit (the group of bones that make up the eye socket), sphenoid bone, ethmoid bone and maxilla.
The main functions of the nasal cavity and paranasal sinuses are to:
- filter, warm and humidify the air we breathe
- give you a sense of smell
- make mucus
- lighten the weight of the skull
- vibrate, or resonate, which helps to give your voice a unique sound
- help absorb trauma to the face and forehead to protect the brain from injury