STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Small intestine. Light micrograph of a section through the entire width of the small intestine. The small intestine is where digestion begins and nutrients are absorbed into the blood. The lumen (white, centre) is lined with villi (red), the folds in the intestinal surface that greatly increase the surface area for absorption. The smooth muscle layer beneath the villi (yellow) is used to mix the food as it passes through the lumen. The thick outer layer (orange) is composed of circular and longitudinal muscle tissue, the peristaltic action of which pushes the food along. Magnification: x60 when printed at 10cm wide.
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