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.
Red blood cells, platelets, and plasma proteins cannot pass through the walls of the capillaries. The resulting mixture that does pass through is, in essence, blood plasma without the plasma proteins. Tissue fluid also contains some types of white blood cell, which help combat infection.ed blood cells, platelets, and plasma proteins cannot pass through the walls of the capillaries. The resulting mixture that does pass through is, in essence, blood plasma without the plasma proteins. Tissue fluid also contains some types of white blood cell, which help combat infection.