SUSUMU NISHINAGA / SCIENCE PHOTO LIBRARY SUSUMU NISHINAGA / SCIENCE PHOTO LIBRARY
Blood vessels. Coloured scanning electron micrograph (SEM) of a resin cast of blood vessels from the small intestine. This network of vessels infiltrates the tissue, supplying it with blood. The lumen (interior) of the intestine is at top. The inner wall of the intestine contains folds, called villi, that greatly increase the surface area for the absorption of nutrients. The nutrients pass into the capillaries (the smallest vessels) near the surface and are then carried away by the larger veins and arteries. The cast was made by injecting resin into the blood vessels and then chemically digesting the surrounding tissues.
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