Diarrhée motrice.

The gut is a long convoluted tube, in which food is processed and nutrients, salt and water are absorbed. The degree of absorption depends to a large extent on the degree of contact between the luminal contents and the absorptive epithelium. Motor activity can influence the degree of absorption because it regulates the degree of contact with the epithelium and it may also induce secretion by a reflex mechanism. Many factors that induce diarrhoea are associated with 'abnormal' and highly propagative forms of motor activity that can clear material through the gut, allowing insufficient epithelial contact for absorption. These propulsive motor patterns may be provoked by distension of the gut with fluid, but they can also occur in response to diarrhoeogenic factors when there is minimal distension. Patients who complain of increased frequency, urgency and incontinence but pass normal stool volumes often have an abnormality in the motor activity of the anorectum. Thus, the generation of abnormal or propagated forms of motor activity must be regarded as an important component of the pathogenesis of all types of diarrhoea and an increased stool volume can be regarded as the end result of a vicious spiral (Figure 12) that may start with a primary abnormality in either motor activity or epithelial transport.