About ten billion capillaries lace all body tissues, bringing blood within reach of every cell. They are the smallest blood vessels, microscopic in size, and contain less than five percent of the total circulating blood volume at any one time. Capillaries branch off from the metarterioles which connect arterioles with venules. The capillaries have thin walls, only one cell thick, across which oxygen and metabolic exchanges take place. As blood flows through the capillaries in the lungs, it changes from venous blood to arterial blood by unloading carbon dioxide and picking up oxygen. Its colour changes in the process from a deep crimson to a bright scarlet. As blood flows through tissue capillaries, it changes back from arterial blood to venous blood. The oxygen leaves the blood to enter cells, and the carbon dioxide leaves the cells and enters the blood. Research Capillaries
Abbreviations
Medicine
Research Capillaries