Small intestine

From Free net encyclopedia

At they hi 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 the length of the large intestine), 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.

1 Functions
2 Small Intestine Disorders
3 References
4 See also
5 External Links

[edit]

Functions

In the small intestine, proteins are changed into amino acids; fats are changed into fatty acids; and carbohydrates are changed into glucose. The small intestine is also the place where the most chemical digestion takes place.(From Encyclopædia Britannica School Edition)

The largest amount of water from the chylus (the substance that comes from the stomach) is absorbed in the small intestine.

[edit]

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
gastric dumping syndrome
infectious diseases
mesenteric ischemia
short bowel syndrome

[edit]

References

Solomon et. al (2002) Biology Sixth Edition, Brooks-Cole/Thomson Learning ISBN 0-03-033503-5

[edit]

External Links

Small Intestine from the Gray's Anatomy eBook

Digestive system - edit
Mouth \| Pharynx \| Esophagus \| Stomach \| Pancreas \| Gallbladder \| Liver \| Small intestine (duodenum, jejunum, ileum) \| Colon \| Cecum \| Rectum \| Anus