Anatomy of the small intestine

The small intestine (small bowel) commences at the pyloroduodenal junction and ends at the ileocaecal junction. It comprises, successively, the duodenum, jejunum and ileum. The principal function of the small intestine is the digestion and absorption of ingested food, electrolytes and vitamins. This important functional specialization is reflected in the enormous surface area of the small intestinal mucosa which is the result of the extensive and wavy infolding of the mucosal lining along the entire length of the small intestine. As might be expected from its very active role as a secretory and absorptive viscus, the small intestine has a rich blood supply. This is derived chiefly from the superior mesenteric artery via its inferior pancreaticoduodenal, jejunal and ileal branches. Accompanying these arterial branches are corresponding venous tributaries that carry venous blood to the superior mesenteric vein and thence to the portal vein. Developmental anomalies, mechanical obstruction and inflammatory disease affect the small intestine far more commonly than do neoplastic conditions.