Contracted heart muscle fibre with a small capillary passing near the muscle fibre, coloured scanning electron micrograph (SEM). Numerous capillaries course through the heart muscle. Capillaries are the small blood vessels (including lymph vessels) that make up the microcirculation of the human body. Their endothelial linings are only one cell layer thick. These microvessels, measuring around 5 to 10 micrometres in diameter. They connect arterioles and venules, and assist the exchange of water, oxygen, carbon dioxide, and many other nutrients and waste substances between the blood and the tissues surrounding them. Capillaries do not function on their own, but instead in a capillary bed, an interweaving network of capillaries supplying organs and tissues. Magnification: x1, 000 when shortest axis printed at 25 millimetres. |