GASTROINTESTINAL SENSATION

The human colon serves to absorb water and electrolytes, store intraluminal contents until elimination is socially convenient, and salvage nutrients after bacterial metabolism of carbohydrates that have not been absorbed in the small intestine. These functions are dependent on the colon's ability to control the distal progression of contents; in healthy adults, colonic transit normally requires several hours to almost 3 days for completion. There are differences in colonic structure and function even among mammals1; unless otherwise stated, this chapter will focus on the physiology of colonic function in humans. Although the colon is regarded as a single organ, there are regional differences between the right and left colon, indicated in Table 144.1. The right and left colon are derived from the embryologic midgut and hindgut, and the junction is located just proximal to the splenic flexure.