Capillaries are the smallest of a body's blood vessels, measuring 5-10 μm. They connect arteries and veins, and most closely interact with tissues. Capillaries have walls composed of a single layer of cells, the endothelium. This layer is so thin that molecules such as oxygen, water and lipids can pass through them by diffusion and enter the tissues. Waste products such as carbon dioxide and urea can diffuse back into the blood to be carried away for removal from the body. Capillary permeability can be increased by the release of cer ...
