Increased secretion can result from stimulated secretion of chloride from crypt cells. In addition, fluids and electrolytes may be secreted into the lumen. When luminal contents are hyperosmolar, fluid is secreted into the lumen to restore osmotic equilibrium. Diarrhea can result from unabsorbed carbohydrates, as in lactose intolerance, when the products of bacterial fermentation impose an osmotic load on the colon. When transit is too rapid, absorption time is decreased and diarrhea can result, which explains the diarrhea seen in hyperthyroidism.
Diarrhea caused by rapid transit is seen after gastric resection or vagotomy.
Cholera toxin stimulates large volumes of saline secretion by directly affecting crypt cells. Salmonella and toxigenic Escherichia coli also produce toxins that increase secretion. Morrison syndrome, or pancreatic cholera syndrome. In the colon, increased secretion can result from unconjugated bile salts that reach the colon as a result of ileal disease.