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.
1 capillaries are tiny, thin-walled vessels which form a network to take blood through the organsand tissues. 2  veins collect blood from the capillaries in the body and return the blood to the heart.3  The wall of the veins are thin, the blood is at a much lower pressure.rteries, veins and capillaries. There are three main types of blood vessels: 1  arteries take blood away from the heart to the body organs and tissues. 2  The artery wall is thick and muscular so it can withstand the high pressure of the blood being pumped directly from the heart.