Small Intestine

figure 48-13

Although the small intestine is nearly 7 m long, only the first 25 cm are involved in digesting food.The rest is involved in the absorption of nutrients. Villi, as shown in the SEM (137x) and the diagram, expand the surface area of the small intestine to allow greater absorption of nutrients.

Small intestine -

If the small intestine were stretched to its full length, it would be nearly 7 m (about 21 ft) long. The duodenum, the first section of this coiled tube, makes up only the first 25 cm (about 10 in.) of that length. The jejunum (jee-JOO-nuhm), the middle section, is about 2.5 m (about 8 ft) long. The ileum, which makes up the remaining portion of the small intestine, is approximately 4 m (about 13 ft) in length. As shown in Figure 48-13, the entire length of the small intestine lies coiled in the abdominal cavity.

Secretions from the liver and pancreas enter the duodenum, where they continue the chemical digestion of chyme. When the secretions from the liver and pancreas, along with the chyme, enter the duodenum, they trigger intestinal mucous glands to release large quantities of mucus. The mucus protects the intestinal wall from protein-digesting enzymes and the acidic chyme. Glands in the lining of the small intestine release enzymes that complete digestion by breaking down peptides into amino acids, disaccharides into monosaccharides, and fats into glycerol and fatty acids.

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