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.
Veins carry blood from the heart to the body. Capillaries are made of very thin walls. The walls have small openings through which leukocytes (white blood cells) and plasma (liquid part of blood) can leak out to form tissue fluid. The lumen is very small (10 micrometers across) so capillaries can fit into tiny spaces.eins carry blood from the heart to the body. Capillaries are made of very thin walls. The walls have small openings through which leukocytes (white blood cells) and plasma (liquid part of blood) can leak out to form tissue fluid. The lumen is very small (10 micrometers across) so capillaries can fit into tiny spaces.