In biology the small intestine is the part of the gastrointestinal tract between the stomach and the large intestine (colon). In humans over 5 years old it is about 7m long. It is divided into three structural parts: duodenum, jejunum and ileum. Food from the stomach is allowed in to the duodenum by a muscle called the pylorus, or pyloric sphincter, and is then pushed through the small intestine by a process of muscular contractions called peristalsis.

The small intestine is the site where most of the nutrients from ingested food are absorbed. There are microscopic finger - like projections called villi covering the small intestinal walls which increase surface area for absorption. Each villus contains a lacteal and capillaries. The lacteal absorbs the digested fat into the lymphatic system which will eventually drain into the circulatory system. The capillaries absorb all other digested nutrients.

Small Intestine Disorders

(see also gastroenterology)

• small intestine obstruction ("high" mechanic ileus)
  • volvulus
  • obstruction from external pressure
  • obstruction by masses in the lumen (foreign bodies, bezoar, gallstones)
• paralytic ileus
• Crohn's disease
• celiac disease
• carcinoid
• Meckel's Diverticulum
• dumping syndrome
• infectious diseases
  • giardiasis
  • ascaridosis
  • tropical sprue
• ischeamic injury
• short bowel syndrome