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The sinuses are normally hollow air spaces within the bones surrounding the nose.

Sinus types

There are four sets of paired sinuses, named for the facial bones where they are located:

  • Maxillary: within the cheek bone underneath the eyes
  • Frontal: in the forehead above the nose and eyes
  • Ethmoid: complex labyrinth of sinus cells and passages between the eyes, further divided into anterior and posterior
  • Sphenoid: located behind the eyes and ethmoid sinuses

Sinus anatomy

Each of the sinuses is an enclosed space that normally drains through an ostium, or opening. All mucus produced within the sinuses is normally propelled toward the natural ostium.

The nasal septum separates the right and left nasal passages and is composed of cartilage in the front and bone in the back, sandwiched between mucous membrane of the nose. Deviated septums are common and can cause nasal obstruction.


The turbinates are normal outgrowths of the nasal sidewall that are shaped to maximize surface area and thus optimize the functions of the nose which will be discussed in the next section.

There are generally three turbinates: inferior, middle and superior, each of which has a cleft underneath termed a meatus.

Specific flow patterns exist with each meatus:

  • The nasolacrimal duct, which drains tears from the eyes, enters into the inferior meatus
  • The maxillary, anterior ethmoid, and frontal sinuses drain into the middle meatus
  • The posterior ethmoid sinuses drain into the superior meatus
  • The sphenoid sinus drains opposite the superior meatus, into the sphenoethmoid recess

Nasal and sinus functions

The nose and sinuses have several important functions of warming, humidifying and filtering the air we breathe.

The primary respiratory goal of the nose is to deliver air of optimal temperature, humidity and cleanliness to the lungs.

A mucus blanket is produced which traps foreign particles, and small hair cells called cilia propel this mucus from the nose and sinuses ultimately toward the throat as a defense mechanism against micro-organisms and allergens.

Olfaction, or sense of smell, is accomplished by receptors that reside high in the nose and sinuses, just below the bone separating the brain from the sinuses. The sinuses are also shock absorbers that provide protection in head injuries, and have a role in vocal quality and resonance.

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