Anatomy of the small intestine

Anatomy of the small intestine

The longest part of the digestive system, where most of the digestion and absorption takes place.



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  • - It is the last part of the hindgut and the digestive system. It absorbs water and plays an important role in forming the stool.
  • - Feces is expelled from the body through it. This process is controllable by two ring-like muscles, the anal sphincters. The internal anal sphincter consists of smooth muscle, while the external anal sphincter is a voluntary striated muscle.


The human digestive system can be divided into an upper and a lower tract.

The stomach, where proteins are digested, is the final part of the upper digestive tract. From here the content of the intestines proceed to the small intestine.

Here the enzymes in the intestinal juice and pancreatic juice break down the essential nutrients, that is, proteins, carbohydrates and fats. Intestinal juice is produced by the glands of the small intestine, while the pancreas secretes pancreatic juice. The bile, produced by the liver and stored in the gallbladder, is also emptied into the small intestine. The bile does not contain digestive enzymes; it emulsifies fat drops to aid in their digestion.

The outer layer of the small intestine is the serous membrane. Under this layer, there are layers of longitudinal and circular smooth muscle. The synchronized motion of these two muscle layers ensures the peristaltic motion of the stomach; it mixes and propels content of the intestines. The digestive system is lined by a mucous membrane, which consists of a thin layer of smooth muscle, connective tissue and epidermis. The glands that secrete the intestinal juice are embedded in the mucous membrane. Circular folds increase the absorptive surface of the small intestine.

Microvilli and villi further increase the absorptive surface of the small intestine.

Carbohydrates, and amino acids released by the digestion of proteins are absorbed into the blood vessels, while lipids are absorbed into the lymph vessels.

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