Digestion and absorption can take place only in the aqueous milieu of digestive secretions.

Synthesis and secretion of these fluids represent a well-controlled process regulated by endocrine» paracrine, and neural events. The total volume of digestive secretions is large, with the daily amount substantially larger than the volume of fluid ingested over a similar period. In addition, most of the digestive secretions have a relatively large concentration of electrolytes. This large outpouring of fluid and electrolyte into the gut makes reabsorption of these secretions imperative if fluid and electrolyte homeostasis of the body is to be maintained. Indeed, one of the major life-threatening ramifications of digestive diseases is the loss of water and electrolytes from the body caused by inadequate reabsorption of digestive secretions.