Atelectasis (/ËÃ¦táµ»ËlÉktÉsáµ»s/ uses combining forms of atel- + ectasis, from Greek: á¼ÏÎµÎ»Î®Ï, incomplete + á¼ÎºÏÎ±ÏÎ¹Ï, extension) is the collapse or closure of a lung resulting in reduced or absent gas exchange.
A single capillary is so small that it allows only one blood cell to flow through it at a time. The capillary walls are also very small, only one cell thick. These thin walls easily allow water, oxygen, carbon dioxide, and other nutrient and waste substances to exchange between blood cells and the surrounding tissue.
Arteries carry oxygenated blood away from the heart, to the cells that need them. Veins carry blood containing carbon dioxide back to the heart after the oxygen has been given to the cells. Capillaries are the thinnest arteries and veins.They are only one cell wide. As the blood cell passes through the very thin capillary, the cells on either side are given oxygen and carbon dioxide is taken from them. Therefore, the capillaries connect the arteries and veins.apillaries are the thinnest arteries and veins. They are only one cell wide. As the blood cell passes through the very thin capillary, the cells on either side are given oxygen and carbon dioxide is taken from them. Therefore, the capillaries connect the arteries and veins.