DAVID SCHARF / SCIENCE PHOTO LIBRARY DAVID SCHARF / SCIENCE PHOTO LIBRARY
Scanning electron micrograph of the wall of the human duodenum, showing the many tiny folds, known as villi, which project 0.5 to 1 mm out into the intestinal lumen. These folds greatly increase the effective absorptive and secretory surface of the mucosa (mucus membrane) which lines the small intestine. The human small intestine is about 6 metres in length and is divided into three sections: the duodenum (which has long, ridge-like villi), the jejunum (with shorter, tongue-like villi) and the ileum (with finger-like villi). Magnification: x75 at 8x10 inch size.
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