Absorption and Elimination
Visible Body
Peristalsis creates propulsion: How food moves through the alimentary canal.
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1. Villi That Line the Walls of the Small Intestine Absorb Nutrients

Villi that line the walls of the small intestine absorb nutrients into capillaries of the circulatory system and lacteals of the lymphatic system. Villi contain capillary beds, as well as lymphatic vessels called lacteals. Fatty acids absorbed from broken-down chyme pass into the lacteals. Other absorbed nutrients enter the bloodstream through the capillary beds and are taken directly to the liver, via the hepatic vein, for processing.

2. The Large Intestine Completes Absorption and Compacts Waste

Chyme passes from the small intestine through the ileocecal valve and into the cecum of the large intestine. Any remaining nutrients and some water are absorbed as peristaltic waves move the chyme into the ascending and transverse colons. This dehydration, combined with peristaltic waves, helps compact the chyme. The solid waste formed is called feces. It continues to move through the descending and sigmoid colons. The large intestine temporarily stores the feces prior to elimination.

3. Defecation Eliminates Waste From the Body

The body expels waste products from digestion through the rectum and anus. This process, called defecation, involves contraction of rectal muscles, relaxation of the internal anal sphincter, and an initial contraction of the skeletal muscle of the external anal sphincter. The defecation reflex is mostly involuntary, under the command of the autonomic nervous system. But the somatic nervous system also plays a role to control the timing of elimination.