The Digestive System
The substance secreted by the liver and stored in the gall bladder and released into the small intestines for the emulsification of fats is bile.
From the duodenum, the food passes through the next two parts of the small intestines, the jejunum and the ileum. The process by which food moves through the intestines (peristalsis) is made possible by involuntary wavelike contractions of the smooth muscles in the intestinal wall.
The small intestines is where the majority of absorption takes place. The nutrients are absorbed into tiny lymph vessels called lacteals, and are passed to a larger vein, the portal vein, to the liver. The liver breaks down any toxins that may be present and prepares the nutrients for release into the bloodstream. The bloodstream carries the nutrients to every cell in the body, where they are used for energy and for tissue building and repair.
From the small intestines, the remaining material, which by now is mostly nondigestable fiber, water and waste, is passed through yet another sphincter valve, the ileocecal valve, to the large intestine or colon. In the colon, any remaining water and electrolytes are absorbed, and the waste material is retained until it is time for it to be evacuated from the body through the rectum and anus. (For more on the colon see the lesson on the Intestinal System.)
The sphincter valve located between the small intestines and the large intestines (colon) is known as the _____________.
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