Always in motion is the future.

GE 345: Week 6

Large Intestine

Updated by Tracey 9 August 02

In the colon, water and electrolytes are reabsorbed from the chyme, and fecal matter is stored until it can be expelled. Colon movements are typically fairly sluggish, since its functions don't require intense movements. Peristaltic waves are rare in the colon, and are mostly replaced by haustral contractions, similar to segmentation in the small intestine, and mass movements, a modified form of peristalsis, in which a large mass of fecal matter is propelled toward the colon. These movements occur one to three times per day. Defecation is typically initiated by reflex.

The dominating secretion in the colon is mucus, which contains large amounts of bicarbonate ions. Mucus protects the colon wall and holds fecal matter together. Large quantities of water an electrolytes may be secreted when a section of the large intestine becomes irritated, acting to dilute the irritants and promote movement of the feces toward the anus, usually resulting in diarrhea.

Most of the water and electrolytes passing into the colon are absorbed, leaving about 50-200 ml of fluid to be excreted in the feces. Most absorption is in the proximal half (absorbing colon). The distal colon is primarily storage. Bacterial activity in the colon forms substances such as vitamans K, and B₁₂, thiamine, riboflavin, and various gasus contributing to flatus.