State three features of alveoli which enables them to perform their function.
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Answer:
Little sacs for oxygen
Alveoli are tiny air sacs in your lungs that take up the oxygen you breathe in and keep your body going. Although they’re microscopic, alveoli are the workhorses of your respiratory system.
You have about 480 million alveoli, located at the end of bronchial tubes. When you breathe in, the alveoli expand to take in oxygen. When you breathe out, the alveoli shrink to expel carbon dioxide.
How alveoli work
There are three overall processes involved in your breathing:
- moving air in and out of your lungs (ventilation)
- oxygen-carbon dioxide exchange (diffusion)
- pumping blood through your lungs (perfusion)
Although tiny, the alveoli are the center of your respiratory system’s gas exchange. The alveoli pick up the incoming energy (oxygen) you breathe in and release the outgoing waste product (carbon dioxide) you exhale.
As it moves through blood vessels (capillaries) in the alveoli walls, your blood takes the oxygen from the alveoli and gives off carbon dioxide to the alveoli.
These tiny alveoli structures taken all together form a very large surface area to do the work of your breathing, both when you’re at rest and when you are exercising. The alveoli cover a surface that measures more than 1,076.4 square feet (100 square meters).
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 1.3 to 2.1 gallons (5 to 8 liters) of air per minute. When you’re at rest, the alveoli send 10.1 ounces (0.3 liters) of oxygen to your blood per minute.
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.
Alveoli and your respiratory system
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 word alveolus comes from the Latin word for “little cavity.”
Alveoli in cross-section
The alveoli are organized into bunches, each bunch grouped is what’s called the alveolar sac.
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 0.2 millimeters in diameter (about 0.008 inches).
Each alveolus is cup-shaped with very thin walls. It’s surrounded by networks of blood vessels called capillaries that also have 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 0.00004 inches (0.0001 centimeters).
About alveoli cells
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.