In biology the small intestine is the part of the gastrointestinal tract between the stomach and the large intestine. In adult humans 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 ingesteed food is absorbed. There are microscopic finger-like projections called villi covering the small intestinal walls which increase surface area for absorption.

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
  • ischeamic injury