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.
Capillaries are the smallest of all blood vessels and form the connection between veins and arteries.As arteries branch and divide into arterioles and continue to reduce in size as they reach the muscle they become capillaries.apillaries have very thin walls comprised only of endothelial cells, which allows substances to move through the wall with ease. Capillaries are very small, measuring 5-10 micrometres in width.