What are the Sinus Cavities?

Sinus cavities are hollow areas in the head. They are an empty space.

It is unlike other parts of the body because a sinus is not something that a surgeon could operate on and take out of your body and lay on the table. It is an empty cavity filled with air.

The paranasal sinuses are lined with a mucous membrane that connects to the nose. The mucus that is produced should escape through a very small drainage channel called the ostia. To function properly, the drainage must be continuous and there must be a free exchange of air between the nose and the sinuses.

Drainage occurs because of tiny hair-like filaments called cilia. The mucus rest on top of the cilia and cells that make up the mucous membrane. The cilia sweeps back and forth at a rate of about 6 to 20 beats per second. This moves the mucous blanket along. The cilia can clear the sinuses in about 10 minutes.

The mucus drains into the nose and from there moves to the back of the throat. It gets swallowed and the stomach acids and enzymes neutralize the bacteria and viruses. It disposes the foreign substances that it has caught from our breathing.

If for any reasons the air exchange stops or blockage prevents the sinus cavities from draining, problems begin to develop. The trapped air and the moisture from the mucus will create an ideal condition for viruses and bacteria to multiply to an unhealthy level. If the blockage persist, infections will likely develop.

There are four pairs of sinuses called the paranasal sinuses. 'Para' comes from the Greek word meaning around or near. 'Nasal', of course, refers to the nose. Sinus comes from the Latin work meaning hollow place.

Image courtesy of Wikipedia

1. FRONTAL
2. ETHMOID
3. SPHENOID
4. MAXILLARY

The Anatomy of the Paranasal Sinuses

Frontal Sinuses

Location: The Frontal sinuses are located just above the nose in the forehead and between the eyes. They are directly in front of the brain. The back wall of the frontal sinuses form the bone that separates them from the brain.
Drainage: They drain into the middle turbinate.
Pain: Inflammation can cause tenderness to the eyes.
At Birth: Not usually present at birth. Frontal sinuses begin to grow around age five. Full development is found during the teenage years. The pair of frontal sinuses are not always found to be the same size and their size can vary widely from person to person.
NOTES: The second largest cavities are the two frontal sinuses.

Ethmoid Sinuses

Location: Located immediately behind the eyes and behind the bridge of the nose.
Drainage: They drain into the middle turbinate. What makes them unique from the others is that the maxillary and frontal sinuses first drain through them before reaching the nose. As a result, a problem in drainage with the ethmoids can cause other sinuses to get clogged. Because the frontal, maxillary and ethmoid sinuses all drain to the same area in the nose, that shared drainage area is known as the ostiomeatal complex.
Pain: Infection in the ethmoid sinuses may feel like ache or pressure between the eyes. Because of how the sinuses drain, infection or inflammation in the ethmoid sinuses may quickly affect the maxillary and frontal sinus. Congestion usually quickly follows when there are problems from the ethmoids.
At Birth: Ethmoid sinuses are present at birth and can continue to grow and reach full development at around the age of twelve. The development is different in each person. In fact, the ethmoid sinuses are thought to be as unique to that person as their fingerprint.
NOTES: Ethmoids are not a single pair of sinuses. They consist of seven to fifteen little chambers and each cavity has its own separate small drainage opening into the nose. Thus, they are considered the smallest of the sinus cavities.

Sphenoid Sinuses

Location: The Sphenoid sinuses are located behind the nose and behind the eyes and at the base of the brain. They are the pair of sinuses that are the deepest inside the head.
Drainage: They drain along the posterior wall of the nasal cavity into the pharynx.
Pain: They lie in very close association to the optic nerve which controls vision. Inflammation here can cause pain to the eyes and also on top or in the back of the head.
At Birth: Sphenoid sinuses appears as small pits at birth and remain underdeveloped until around the ages three to five. They begin to grow and gradually enlarge to the size of large grapes and reach full development during the late teenage years.
NOTES: The sphenoid sinuses are the third largest of the sinus cavities. Because of how deep within the head in which they lie, the sphenoid sinuses are more difficult to examine and infections can sometimes go undetected.

Maxillary Sinuses

Location: The Maxillary sinuses are located behind the cheekbone, extending from just beneath the eyes to above the upper teeth on either side of the nose. In some people, the roots of the teeth of the upper jaw often protrude into the floor of the maxillary sinus.
Drainage: They drain into the nose beneath the middle turbinate.
Pain: Due to the close proximity to the upper teeth, infection in the maxillary sinuses can feel like a toothache. Pain can also be felt in the cheek because of the infraorbital nerve which (supplies sensation to the cheek) runs along the side of this sinus cavity.
At Birth: They are moderately developed at birth and develop very early in life. They experience a second increase in size between ages 7 to 12 when the permanent teeth develop.
NOTES: Maxillary sinuses are the largest of the sinus cavities.These sinuses are located close to the teeth. These sinuses seem to cause people the most discomfort. One explanation for this might have to do with how the maxillary sinuses drain. The opening hole for drainage is not found at the bottom of the sinus. The opening is at the top of the sinus. Thus, it is harder for the cilia to move the cilia to move the mucus up and against gravity.

Why We Have Sinus Cavities

It is not known for sure why we have sinuses, however, various answers that have been offered are listed below.

The sinus cavities, along with the nose, as part of the upper respiratory tract;

• Lightens the weight of the skull:
If the empty areas were filled with bone or tissue, the neck would have more of a difficult time holding up the head. Air pockets makes the skull lighter.
• Aids in speech:
They serve as a resonance chamber to aid the voice box in giving sound. Note how your voice changes when you talk and pinch you nose shut at the same time.
• Humidifies:
They add humidity to the air that we breathe. Without doing so, dry air would irritate the lungs.
• Insulation:
They serve as an insulator which also warms the base of your brain and warms the air that we breathe.
• Protects the lungs:
This is accomplished as a 'pre-filter.' The mucus catches particles that we breathe in and the mucous membrane (along with cilia) disposes of them.
• Protects the brain:
They act as an air bag during a blow to the face. Sinuses can absorb the impact of a blow to the face resulting in a decrease of injury to the deeper structures. Softening a blow may prevent the skull from a fracture.
• Protects the body:
they contribute around 10 percent of the mucus to the nose and throat. This supply of mucus contains bacteria-destroying enzymes. As a result, the nose is better able to collect, neutralize, and to flush out invading organisms and pollutants.
• Regulates temperature:
To protect the lungs, the nose and sinuses cools the hot air that we breathe in and warms the cold air.
• Improves taste and smell:
Having more space for odor molecules to linker, the smell receptors can do a better job. Note how you loose taste and smell when you have a cold, nasal allergies, or sinusitis.

The nose and sinus cavities are always at work, protecting the lungs from harm. The sinus cavities must be working properly in order to prevent infection from taking place. For those who have sinusitis or some form of allergic rhinitis, getting the mucous blanket to flow properly and getting the air exchange between the nose and sinuses back to normal is an important step in regaining your health and quality of life.

To learn more about the sinus cavities, the MedicineNet.com website provides good information along with related topics.

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