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 very small in size because they need to have a large surface area so they are able to transport blood all around the body. Blood cells must pass in singl â¦ e file through the capillaries as they are so small.16 people found this useful. Ahmadbtm. Capillaries are very small in size because they need to have a large surface area so they are able to transport blood all around the body. Blood cells must pass in singl â¦ e file through the capillaries as they are so small. 16 people found this useful. Ahmadbtm.