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, which are the smallest and most numerous blood vessels in the human body (ranging from 5 to 10 micrometers in diameter and numbering around 10 billion) are also the thinnest walled vessels; an inner diameter of 5 um is just wide enough for an erythrocyte to squeeze through.icrocirculation is a term coined to collectively describe the flow of blood through arterioles, capillaries and the venules (Fig. 2). (click image for larger view). Figure 1. The major paths of blood flow through pulmonary and systemic circulatory systems.