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.
In conclusion, the arteries carry oxygenated blood away from the heart, and due to the high pressure of this blood the arteries have thick wall, which contain many muscle fibres. The veins carry deoxygenated blood to the heart and because blood is of a lower pressure, have thinner walls consisting of less muscle fibres. intend to explore the structure and function of arteries, veins and capillaries. When an artery branches into smaller and smaller vessels, eventually the blood vessel is too small to see with the naked eye. At that point, it is called an arteriole. Likewise, a venule is a microscopic vein.