Alveoli

Role in the respiratory system.

The final branches of the respiratory tree, alveoli are where oxygen from the air enters your blood, and carbon dioxide from your body is expelled back into the air.

How they work.

Air enters the body through the nose or mouth, passes through the larynx, down the trachea, and into our lungs. Once it is in your lungs, air goes through a maze of smaller and smaller bronchial tubes until it reaches clusters of tiny sacs the alveoli. In appearance they are somewhat like bunches of grapes.

Size and where they live.

These alveoli are tiny, but your lungs are simply packed with them an estimated three hundred million per lung, all required to ensure that your body gets the oxygen it needs.

Once it is in your lungs, the blood has to get into your blood. The alveoli are the primary gas exchange units of the lung. Quite simply, they are the point where the gas-blood barrier is thin enough to permit rapid gas exchange.

To get into the blood, oxygen is diffused through the alveolar epithelium, a thin interstitial space, and the capillary endothelium.

Role also has to be reversed.

That is only half the process of course this process also has to work in reverse in order to allow CO2, a waste product carried by the blood, to be expelled back into the lungs, and thus out of the body when we exhale.