Friday, March 1, 2013

ALVEOLI

The alveoli
Alveoli are tiny grape-like sacs. There are two kinds of alveoli, those that exchange gases in the lungs, and those that turn blood into breast milk in the breast. The singular of alveoli is one alveolus.
"Alveoli {in the breast} are grape-like clusters of glandular tissue in which milk is synthesized from blood. Aveoli cells secrete milk. They are surrounded by a network of band-like myoepithelial cells, which cause the alveoli to contract when stimulated by the oxytocin released during the let-down, or milk-ejection, reflex. This action expels the milk into the ductules and down into the ducts."[1]
Alveoli in the lungs exchange oxygen with red blood cells when the heart's Sinoatrial and Atrioventricular nodes send electric signals to the hearts ventricles. The right side of the heart then contracts twice,[source?] sending blood shooting into the pulmonary circulatory system, where capillary beds are located in the lungs. The Alveoli then exchange oxygen and discard carbon dioxide with the red blood cells, which then return to the heart's left atrium. When you breathe out, the body delivers carbon dioxide to the alveoli, and you release it in your exhalation. When you breathe in, oxygen fills the alveoli and then enters the blood, so it can be delivered to the rest of the body. In asthma there is no damage to the alveoli, which is different from another common lung disease which is called: chronic obstructive pulmonary disease, in which alveoli are damaged. A network of blood capillaries surround walls of each alveolus.The walls are extremely thin(one cell thick)and moist,thus allowing gaseous diffussion through them. There are over 300 million alveoli in each lung. If you were to spread one person's alveoli across a tennis court, they would cover over half the court!
The alveoli also help for the lungs to keep out unwanted pathogens and viruses.

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