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.
The blood-brain barrier is made up of very small blood vessels (capillaries) that are lined with thin, flat endothelial cells. In other parts of the body, endothelial cells have small spaces between them that allow substances to move in and out of the capillary so they can reach other cells and tissues.In the brain, the endothelial cells are packed tightly together so substances cannot pass out of the bloodstream into the brain.n other parts of the body, endothelial cells have small spaces between them that allow substances to move in and out of the capillary so they can reach other cells and tissues. In the brain, the endothelial cells are packed tightly together so substances cannot pass out of the bloodstream into the brain.