In latin, sinus means a fold, or pocket, particularly the front pocket of a roman toga. Humans have many sinus cavities in the body:
- Maxillary – directly under the eyes, largest of the nasal sinuses
- Frontal – just above the eyes, part of the hard forehead
- Ethmoid – air cells in the ethmoid bone between the nose and eyes
- Sphenoid sinuses – are in the sphenoid bone at the base of the skull, under the pituitary gland
Anal Sinuses – separate the columns of the rectum
Dura Venous Sinuses – venous channels found between layers of dura mater in the brain
It becomes pretty obvious after a brief review that the sinuses are imperative to breathing, heart function, and homeostasis within an environment. This is why sinus infections will often flair with allergic reactions, or major changes in environment.
Currently the evolutionary role of the sinuses are in huge debate (meaning we really don’t understand their complete functionality as it applies to adapting to the environment), but there are a few theories:
- Decreasing the relative weight of the front of the skull, and especially the bones of the face.
- Increasing resonance of the voice.
- Providing a buffer against blows to the face.
- Insulating sensitive structures like dental roots and eyes from rapid temperature fluctuations in the nasal cavity.
- Humidifying and heating of inhaled air because of slow air turnover in this region.
- Regulation of internasal and serum gas pressures
- Immunological defense
I’ve bolded the few that I think make the most sense: environmental protection against temperature changes (hence runny noses when you fluctuate too quickly between cold and hot), defense against intruding particles in the air (sneezing and allergies), and pressure equilibrium (fluctuations in altitude). But I do think that we have a large amount to learn about how these parts of the body work, questions that Eastern sciences can address, but for which the Western world still has no answer.
Allergy medicine is mostly steroids and stimulants, which solves the problem short-term, but weakens the immune system with just one dosage by killing probiotic organisms already in the body.
Breathing with your nose instead of your mouth is extremely important as it adjusts the air entering the lungs to body temperature, air is humidified, and dust particles are halted from entering the body. When I was in Beijing for 5 days, I breathed almost exclusively from my nose, because I was afraid that the large dust particles would harm my throat.
The nasal cavity then connects to the trachea, which is kind of the second line of defense. It is coated with mucus to either expel or digest particles by lifting them to the pharynx and larynx which are the structures in the throat that lead to the stomach and lungs, respectively.
The air then flows into the bronchi which branch to the left lung and the right lung, where the alveoli exchange oxygen for carbon dioxide. The sinuses are the first purification center for this process to take place, and are a kind of first line of defense for the air entering the body.