Advances in understanding colonic function.

The colon is an organ of conservation that salvages water, electrolytes, and energy. The organization of colonic function is determined by the roles played by the luminal flora, the function of the different mucosal epithelial cell types, immunocompetent cells, and the neuromusculature. These different components of the colon interact with one another and with the colonic flora, and different areas of the colon serve different functions. In the normal adult during the course of a day the colon absorbs approximately 1.5 L of fluid, but under the influence of aldosterone increases up to 5 to 6 L. Diarrhoea occurs when secretion exceeds absorptive processes by either small intestinal secretion overwhelming colonic salvage or salvage being impaired by reduced colonic absorption or increased colonic secretion.