The alveoli cover a surface that measures more than 1, This large surface area is necessary to process the huge amounts of air involved in breathing and getting oxygen to your lungs. Your lungs take in about 1. To push the air in and out, your diaphragm and other muscles help create pressure inside your chest. When you breathe in, your muscles create a negative pressure — less than the atmospheric pressure that helps suck air in. When you breathe out, the lungs recoil and return to their normal size.
Picture your lungs as two well-branched tree limbs, one on each side of your chest. The right lung has three sections lobes , and the left lung has two sections above the heart. The larger branches in each lobe are called bronchi. The bronchi divide into smaller branches called bronchioles.
And at the end of each bronchiole is a small duct alveolar duct that connects to a cluster of thousands of microscopic bubble-like structures, the alveoli. The alveoli touch each other, like grapes in a tight bunch. The number of alveoli and alveolar sacs are what give your lungs a spongy consistency. Each alveolus singular of alveoli is about 0. Each alveolus is cup-shaped with very thin walls.
The oxygen you breathe in diffuses through the alveoli and the capillaries into the blood. The carbon dioxide you breathe out is diffused from the capillaries to the alveoli, up the bronchial tree and out your mouth.
The alveoli are just one cell in thickness, which allows the gas exchange of respiration to take place rapidly. The wall of an alveolus and the wall of a capillary are each about 0.
The outside layer of alveoli, the epithelium, is composed of two types of cells: type 1 and type 2. Type 1 alveoli cells cover 95 percent of the alveolar surface and constitute the air-blood barrier. Type 2 alveoli cells are smaller and responsible for producing the surfactant that coats the inside surface of the alveolus and helps reduce surface tension.
The surfactant helps keep the shape of each alveolus when you breathe in and out. The type 2 alveoli cells can also turn into stem cells. If necessary for repair of injured alveoli, alveoli stem cells can become new alveoli cells. They have very thin walls for gases to be absorbed through. An individual air sac is called an alveolus. The layer of moisture in the alveoli allows gases to dissolve so that they can diffuse quickly.
The alveoli have a very large total surface area and a very good blood supply, provided by the dense network of capillaries that surround them. There is an exchange of gases between the alveoli and their surrounding capillary blood vessels.
Oxygen diffuses from the alveoli into the blood. Carbon dioxide diffuses from the blood into the alveoli. These three features are particularly important to our lungs for efficient gas exchange. The lungs are a pair of elastic, spongy organs used in breathing. In humans the lungs take up a lot of the chest cavity. They are located just behind, and to either side of, the heart. They extend down from the collarbone to the diaphragm the muscular wall between the chest cavity and the abdominal cavity.
In adult humans each lung is 25 to 30 cm. The right lung is somewhat larger than the left lung because it has three lobes , or sections, whereas the left lung has only two.
When we breathe, the air travels to the lungs through a series of tubes and passages. The air enters the body through the nostrils or the mouth. It travels down the throat to the windpipe.
Inside the chest cavity the windpipe divides into two branches, called the right and left bronchial tubes that enter the lungs. The large bronchial tubes branch into ever smaller tubes, called bronchioles.
These in turn divide into even narrower tubes. Each small tube ends in clusters of thin-walled air sacs, called alveoli. It is the alveoli that receive the oxygen and pass it on to the blood. The alveoli are surrounded by tiny blood vessels, called capillaries.
The alveoli and capillaries both have very thin walls, which allow the oxygen to pass from the alveoli to the blood.
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