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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 5-6m 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.
Although the small intestine is much longer than the large intestine (typically 4-5 times longer), it is referred to as such due to its comparatively smaller diameter. On average, the diameter of the large intestine of an adult human measures approximately 3 times the diameter of the small intestine. Upon viewing accurate diagrams of the digestive system, non-medically trained personnel often initially express bemusement as to why the obviously longer portion of the digestive system is referred to as the small intestine.
Functions
The digestion of proteins into peptides and amino acids principally occurs in the stomach but some also occurs in the small intestine. The small intestine is where the most chemical digestion takes place; peptides are degraded into amino acids; lipids (fats) are degraded into fatty acids and glycerol; and carbohydrates are degraded into simple sugars (e.g., glucose).
The largest amount of water from the chyme (the substance that comes from the stomach) is absorbed in the small intestine.
Small Intestine Disorders
(see also gastroenterology)
- small intestine obstruction ("high" mechanic ileus)
- 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
- gastric dumping syndrome
- infectious diseases
- mesenteric ischemia
- short bowel syndrome
- inguinal hernia
References
Solomon et. al (2002) Biology Sixth Edition, Brooks-Cole/Thomson Learning ISBN 0-03-033503-5
See also
External Links
Dünndarm | Intestino delgado | Maldika intesto | Intestin grêle | Intestino tenue | המעי הדק | Tanko crijevo | Plonoji žarna | Тенко црево | Dunne darm | 小腸 | Tynntarm | Jelito cienkie | Intestino delgado | Тонкая кишка человека | Танко црево | Ohutsuoli | Tunntarm | 小肠
"Small intestine"