The sinuses (say: sy-nus-is) are air-filled spaces found in the bones of the head and face. Sinuses start developing before you are born and some of them keep growing until you're about 20. There are four pairs of sinuses, or eight in all. They are located on either side of the nose in your cheeks, behind and between the eyes, in the forehead, and at the back of the nasal cavity.
Like the inside of the nose, the sinuses are lined with a moist, thin layer of tissue called a mucous membrane (say: myoo-kus mem-brayne). The mucous membranes help moisten the air as you breathe it in. The mucous membrane also makes mucus, that sticky stuff in your nose you might call snot. The mucus traps dust and germs that are in the air we breathe. On the surface of the cells of the mucous membrane are microscopic hairs called cilia (say: sih-lee-uh).
The cilia beat back and forth in waves to clear mucus from the sinuses through a narrow opening in the nose and then move the mucus toward the back of the nose to be swallowed. Gross, huh? If you have a cold or allergies, the membrane gets irritated and swollen and produces even more mucus.
What Do Sinuses Do?
No one is completely sure why we have sinuses, but some researchers think they keep the head from being too heavy. Sinuses are pockets of air, and air doesn't weigh very much. If those pockets were solid bone, your head would weigh more.
Sinuses also give you the depth or tone of your voice. Did you ever notice how funny your voice sounds if your nose and sinuses get stuffy when you have a cold?
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