[Pathophysiology of chronic diarrhea]

The symptom of diarrhoea is defined as an abnormally frequent discharge from the bowel (more than 3 times a day) and a semisolid or fluid consistency of the faecal matter. Diarrhoea is termed chronic when it lasts more than four weeks. Diarrhoea is the result of disturbances in enteral water and electrolyte balance. Increased intestinal motility is usually not the cause but the result of diarrhoea. Transport of water through the gut is dependent on the osmotic gradient between interstitium and gut lumen. The secretion of chloride ions by the cells of the intestinal glands plays a major role in water secretion into the gut lumen, while sodium and potassium absorption in the villous zone of the enterocytes is crucial for enteral water absorption. Enteral water and electrolyte balance is regulated by the autonomic and enteral nervous system, by gastrointestinal hormones and signal messengers of mesenchymal cells. Pathogenetically, one distinguishes between secretory and osmotic diarrhoea. Furthermore, mixed forms of both pathogenic types can occur. The various types can be differentiated clinically and by the "osmotic gap". Diarrhoea can be a symptom of various diseases. Its pathogenesis is illustrated using examples of diarrhoea in pathological bile acid absorption, bacterial infections, carbohydrate malabsorption or disaccharidase insufficiency and in chronic inflammatory bowel disease.