What are Sinuses?

In this article :

What are Sinuses?

we get asked this question more often than you can imagine. People often use Sinus and Sinusitis interchangeably leading to more confusion. We will get to “What is Sinusitis?” in a subsequent post, but first let us address What are Sinuses?”.

Sinuses are inter-connected air-filled spaces in the bones of the face, around the nose region. The largest of these spaces are about an inch wide while the others are much smaller.

Their development starts in the early stages of pregnancy – a 10-week old embryo already has a face and nose, including sinuses (those “early sinuses” are nothing more than tiny air bubbles in the bones surrounding the nasal cavity). Their full development ends approximately at the age of 19 years. As the head and permanent teeth grow throughout childhood and adolescence, sinuses grow as well, and their volume increases. This process is known as Pneumatization.

Each sinus, as well as the canal that connects it with the nasal cavity, is covered with fine lining, exactly the same as the one that covers most of the respiratory tract. The lining contains cells with cilia (fine thread-like structures that continuously move in a whip-like motion – cleaning the lining surface that way) and specialised cells that produce mucus (mucus acts as a medium that traps bacteria, viruses, dust and other particles inside, making the cleaning process easier and more effective).

Now that we have understood the basics of “What are sinuses?”, let us delve a little deeper in understanding the Types of Sinuses.

Our body has four pairs of Sinuses

- What are Maxillary Sinuses?

Maxillary sinuses are located under the eyes, next to the nose and above the teeth in the upper jaw. In some people, teeth roots can reach really close to, or even penetrate into the sinus. Such a close anatomical relation to the teeth can cause the spread of infections from the mouth to the sinus cavity.

- What are Frontal Sinuses?

Frontal Sinuses are located above the eyes, close to the middle line of the face (the imaginary line that splits the face into left and right halves).

- What are Sphenoid Sinuses?

Sphenoid Sinuses are located deep in the face region, behind the eyes and close to the middle line, their relation to the nasal cavity is not as close as that of maxillary and frontal sinuses. Close anatomical relations with eyes and brain is what makes them particularly delicate (especially in terms of inflammation and surgical interventions).

- What are Ethmoid Cells or Sinuses?

Unlike the other three pairs that consist of one (on each side) cavity, Ethmoid(or Ethmoidal) Cells are made of several tiny cavities located between the eyeballs and nasal cavity.

- Are Sinuses normally empty?

Normal, healthy sinuses are empty except for a thin layer of mucus. It is only when our sinuses get infected that they get filled with fluids which we will explain in detail in “What is Sinusitis?”

- So what purpose do these Sinuses serve in the human body?

The exact function of Sinuses has been a matter of debate among doctors for centuries. In the end, they all agreed about one thing – the Paranasal sinuses act as voice resonators which is their primary function. Other than that, the air entering our nose and mouth passes through our Sinuses and the mucus layer helps humidify or moisturize the air before it reaches our lungs. Not just that, this mucus layer also helps protect us from dust, pollutants and micro-organisms.

Also, sinuses lighten the skull which is probably not that important for modern humans, but during millions of years of evolution, this adaptation may have helped us survive as a species.

- What are Paranasal Sinuses?

Paranasal sinuses are cavities inside the bones of the face. Lay people often refer to these structures as sinuses.

Although lay people often think of sinuses as separate structures scattered around the face region, they are actually well-connected with other parts of the upper respiratory tract and make quite a big system of canals and cavities in the face region. Their close anatomical relation to organs such as eyes, brain, and teeth is the reason why every sinus infection requires close medical attention.

Hope we could address your question on "What are Sinuses?". Now let us look at what is Sinusitis.

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Medically reviewed by SinusDoctor,
Dr G V K Chaitanya Rao

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