Breath has always been regarded as our life force, because without air, we cannot exist. As you will recall from previous articles, your heart pumps blood to the lungs (circulatory system) where the blood receives life-giving oxygen and disposes of the toxic carbon dioxide. The mechanics of this exchange however, is the job of the respiratory system, and it happens automatically with each breath.

You can inhale through either your nose or moth, but when the air enters your body through the nose, you receive the additional benefits of your nose's job which is to warm, moisten and filter the air before it moves down your throat. Its those little nose hairs that actually help trap any tiny particles that you've inhaled and keep them from going any further.

Once air has traveled down your throat, it quickly passes from your larynx and goes into your trachea or "windpipe" which, at its end, divides into bronchi, the air passages that connect it to the lungs. Inside each lung, the bronchi divide into bronchioles, smaller airways which look like tree roots. At the end of these bronchioles, little sacs called alveoli play host or the exchange of oxygen for carbon dioxide. Oxygen leaves the sacs and enters the blood via tiny blood vessels. Carbon dioxide leaves the bloodstream and, after passing through the alveoli sacs is ultimately exhaled. Realize how quickly this exchange happens.

When we inhale and exhale, our lungs expand and contract by the action of a muscle just under our chest called the diaphragm and by subsequent motion of the rib cage. When your diaphragm contracts (and the chest cage diameter increases), the air pressure inside your chest is reduced to less than the air pressure outside your body and this action draws air into your lungs. This is inhalation. When the diaphragm expands and relaxes, air is pushed out of your lungs. This is exhalation.

Anything that harms or weakens the lungs or any of its components can result in conditions such as pneumonia, asthma, bronchitis, pleurisy, embolism, tuberculosis, apnea and tumors.