Absorbing nutrients from food is the job of the small intestine. Two major specializations help make absorption more efficient. First, the intestine is a very long tube (up to 25 feet in adult humans) and second, the surface of the tube is highly convoluted by the presence of finger-like projections called “villi” (singular, villus). Each villus is covered with absorptive epithelial cells (green) and has a core that contains blood vessels (red) and muscle (blue). Nutrients are absorbed and processed by the green epithelial cells and secreted from the base of these cells toward the blood vessels. The core muscles then pump the nutrient-rich blood on to the next metabolic organ, the liver. Loss of villi, in celiac disease for example, can cause malabsorption.
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