Diarrhea is a complication of the alimentary or digestive system, a complication we all have faced one time or another. Ivan Damjanov’s Pathology for the Health Professions defines diarrhea as “the frequent passage of loose, watery stools because of intestinal or pancreatic and hepatobiliary disturbances” (Damjanov, 2012). The primary reason why diarrhea occurs is due to an increase in colonic fluid volume in the intestines. The increase in colonic fluid is a result of three physiologic mechanisms, which include active secretion, osmosis, and faulty water reabsorption. Two of three etiologies of diarrhea occur mainly in the small intestine: active secretion and osmosis. Active secretion pertains to bacterial invasions such as Vibrio cholerae, toxins, irritants, and excess bile and fat. According to Dr. Bharucha, diarrhea that’s caused by food poising is because “most enterotoxins block Na+-H+ exchange, which is an important driving force for fluid absorption in the small bowel and colon” (Bharucha, 2007). Osmosis is the passive movement of water. Passive movement of water into the lumen of the intestines is a direct result of high solute concentrations or “unabsorbable, water-soluble solutes that remain in the bowel” (Bharucha, 2007). When these solutes remain in the lumen or bowel, water follows naturally causing an increase in colonic fluid. Laxatives focus on this mechanism to aid in passing of stool. Faulty digestion and poor absorption of the digested material explains the high solute concentration. Improper balances of the normal micro flora can also result in high concentrations of solute in the lumen because some of the bacteria in the gut aids in adequate and sufficient digestion. Therefore a lack there of would hinder proper function. Dr. Bharucha also mentions that “rapid intestinal transit and diminished surface area impair digestion” therefore leading to diarrhea because of an increase in colonic fluid in the intestines (Bharucha, 2007). All three of these mechanisms bring excess unwanted colonic fluid into the intestines. Active secretion through infection such as gastritis, enterotoxins of food poising, and specific drugs cause an increase in colonic fluid. Osmosis of water into the lumen due to insoluble solutes and “sugar intolerance” like being lactose intolerant also cause an increase in colonic fluid. Lastly the inability to of the intestines to function properly because of speedy passage of the bowel in the lumen, disturbances of normal micro flora, and reduced surface area increase in colonic fluid in the intestines because water isn’t reabsorbed as efficiently as it should.