Small Intestine

∆ Small Intestine

The small intestine is the body’s major digestive organ.

• Location. The small intestine is a muscular tube extending from the pyloric sphincter to the large intestine.

• Size. It is the longest section of the alimentary tube, with an average length of 2.5 to 7 m (8 to 20 feet) in a living person.

• Subdivisions. The small intestine has three subdivisions: the duodenum, the jejunum, and the ileum, which contribute 5 percent, nearly 40 percent, and almost 60 percent of the small intestine, respectively.

• Ileocecal valve. The ileum meets the large intestine at the ileocecal valve, which joins the large and small intestine.

• Hepatopancreatic ampulla. The main pancreatic and bile ducts join at the duodenum to form the flasklike hepatopancreatic ampulla, literally, the ” liver-pacreatic-enlargement”.

• Duodenal papilla. From there, the bile and pancreatic juice travel through the duodenal papilla and enter the duodenum together.

• Microvilli. Microvilli are tiny projections of the plasma membrane of the mucosa cells that give the cell surface a fuzzy appearance, sometimes referred to as the brush border; the plasma membranes bear enzymes (brush border enzymes) that complete the digestion of proteins and carbohydrates in the small intestine.

• Villi. Villi are fingerlike projections of the mucosa that give it a velvety appearance and feel, much like the soft nap of a towel.

• Lacteal. Within each villus is a rich capillary bed and a modified lymphatic capillary called a lacteal.

• Circular folds. Circular folds, also called plicae circulares, are deep folds of both mucosa and submucosa layers, and they do not disappear when food fills the small intestine.