Small Intestine Definition

The segment of the gastrointestinal tract immediately following the STOMACH. The small intestine’s three sections – DUODENUMJEJUNUM, and ILEUM – perform about 85 percent of the digestive functions of the gastrointestinal tract.

Food passes from the STOMACH to the duodenum, from the duodenum to the jejunum, and from the jejunum to the ileum. The small intestine loops and folds through the inner abdomen, with the COLON (large intestine) encircling it like a frame. Microscopic extensions, villi, arise from the mucosa, forming peaks and valleys that dramatically increase the surface area of the mucosa.

Conditions that can affect the small intestine

CONDITIONS THAT CAN AFFECT THE SMALL INTESTINE
BOWEL ATRESIACELIAC DISEASE
Crohn’s diseaseGASTROENTERITIS
ILEUSLACTOSE INTOLERANCE
MALABSORPTIONPEPTIC ULCER DISEASE
WHIPPLE’S DISEASE

A meal’s transit time through the 18 or so feet of the small intestine is about 10 hours, during which intestinal mucosa (mucous membrane that lines the intestinal tract) extracts all of the nutrients, many of the electrolytes, and much of the water.

For further discussion of the small intestine within the context of gastrointestinal structure and function, please see the overview section “The Gastrointestinal System.”

See also ANUS; FOOD-BORNE ILLNESSES; INFLAMMATORY BOWEL DISEASE (IBD)IRRITABLE BOWEL SYNDROME (IBS)RECTUM.

Small Intestine – anatomy, parts, problems and function
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