Small Intestine

Small intestine is the longest part of alimentary canal. It extends from the pylorus of the stomach to the junction between cecum and ileum. Much of digestion and absorption of food takes place in the small intestine.

Parts of small intestine:

The small intestine is divided into three parts: Duodenum, Jejunum and Ileum.

Duodenum: It is the first part of small intestine that joins the stomach. It receives openings of the bile and pancreatic ducts. Visit “Anatomy of duodenum” for further details.

Jejunum: It is the second part of small intestine that lies between the duodenum and ileum. It begins at the duodenojejunal flexure of the small intestine and is about 8 feet long. Visit “Anatomy of jejunum and ileum” for more details.

Ileum: It is the last and the longest part of small intestine. It joins the cecum at the ileocecal junction. Visit “Anatomy of jejunum and ileum” for more details.

Digestion in small intestine:

Small intestine is the portion of alimentary canal where most of the chemical digestion takes place. Most of the enzymes responsible for this digestion are produced in the pancreas, and reach it through the pancreatic duct. The enzymes enter the small intestine in response to the hormone cholecystokinin, which is produced by it in response to presence of nutrients.

All of the three major classes of nutrients (proteins, lipids and carbohydrates) undergo digestion in small intestine.

Absorption in small intestine:

Once the chemical digestion is complete, the products are readily absorbed by the small intestine mainly through the process of diffusion. The inner wall, or mucosa of small intestine is covered in folds called plicae circulars, from which project the finger-like microscopic projections known as microvilli. This arrangement greatly increases the surface area of mucosa of small intestine aids in proper absorption of nutrients.