Paranasal sinuses

Definition

Nose and nasal cavities

The air-filled spaces, lined with mucous membrane, within some of the bones of the skull. They open into the nasal cavity. They comprise the frontal sinuses and the maxillary sinuses (one pair of each), the ethmoid sinuses (consisting of many spaces inside the ethmoid bone), and the two sphenoid sinuses.

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Paranasal Sinuses: An Overview

Respiratory system

Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity. These cavities, found within the bones of the skull, are lined with a mucous membrane, facilitating the humidification and warming of inhaled air and contributing to the resonance of the voice. They also play a role in reducing the weight of the skull.

Anatomy of Paranasal Sinuses

Paranasal sinuses are classified into four main groups, each named after the bone in which they are located:

• Frontal sinuses: Located behind the forehead, there is one sinus in each frontal bone, making a pair. They are responsible for draining mucus into the middle meatus of the nose.

• Maxillary sinuses: These are the largest of the paranasal sinuses and are situated in the maxillary bones, beneath the eyes and either side of the nose. They drain mucus into the middle meatus of the nasal cavity.

• Ethmoid sinuses: Found between the nose and the eyes, within the ethmoid bone. They are a complex group of multiple small cavities often referred to as 'ethmoid air cells'. The ethmoid sinuses are further divided into anterior, middle, and posterior groups. These sinuses drain into both the middle and superior meatus of the nasal cavity.

• Sphenoid sinuses: Located deep within the skull behind the eyes, these two cavities sit within the sphenoid bone. They drain into the sphenoethmoidal recess situated above the superior nasal concha.

Function of Paranasal Sinuses

Beyond their structural roles, the paranasal sinuses also serve several vital functions:

• Humidification and Warming: As air passes through the nasal cavity and paranasal sinuses, it gets warmed and humidified, which is crucial for the efficient function of the lungs.

• Resonance: The sinuses play a role in determining the tonal quality of the voice by acting as resonance chambers.

• Protection: They act as a cushion or buffer for the skull, protecting the brain from trauma.

• Immunity: The mucus produced by the sinuses contains antibodies, trapping foreign pathogens and aiding in defending the body against infections.

Clinical Significance

The anatomy and physiology of paranasal sinuses have direct clinical implications:

• Sinusitis: An inflammation or swelling of the tissue lining the sinuses. It can result from viral, bacterial, or fungal infections or allergic reactions.

• Polyps: Non-cancerous growths on the mucous membrane of the sinuses or nose. They can block sinus passages, leading to sinusitis.

• Surgery: Surgical interventions, like Functional Endoscopic Sinus Surgery (FESS), are performed to treat chronic sinusitis or remove polyps.

Summary

Understanding the anatomy, function, and clinical relevance of paranasal sinuses is essential for both clinicians and those interested in the human anatomy. These air-filled cavities not only play a vital role in respiratory and immune functions but also contribute to the unique characteristics of an individual's voice.

See Also

• Nasal cavity
• Skull
• Mucous membrane
• Sinusitis

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