what does the alveoli do

The alveoli are tiny air sacs in the lungs that are responsible for gas exchange between the air we breathe and the blood in our bodies. They are the site where oxygen from the air we inhale enters the bloodstream, and carbon dioxide, a waste product of metabolism, is removed from the bloodstream and exhaled out of the body. The alveoli are organized into bunches, and each bunch is grouped in the alveolar sac. The alveoli touch each other like grapes in a tight bunch, and the number of alveoli and alveolar sacs is what gives the lungs a spongy consistency. Each alveolus is about 0.2 to 0.3 millimeters in diameter and is covered by a network of capillaries. The alveoli move oxygen and carbon dioxide molecules into and out of the bloodstream. The alveoli are lined with thin, squamous, and flat epithelial lining cells that form the structure of the alveoli. They have long cytoplasmic extensions that cover beyond 95% of the alveolar surface, which enables a fast diffusion of gas exchange between the air in the alveoli and the blood in the surrounding capillaries.