Defecation Urge: Function, Tasks, Role & Diseases

The urge to defecate is triggered by mechanoreceptors in the wall of the intestine that register the rising tension as the level of the rectum increases. The receptors send the information via the spinal cord to the central nervous system, where it passes into consciousness. Hemorrhoids often cause persistent urge to defecate.

What is the urge to defecate?

Through the physiological process of defecation, the human rectum empties itself and disposes of indigestible food residues in this way. Intestinal activity after meals carries the intestinal contents toward the rectum with propulsive mass movements called intestinal peristalsis. When the digested intestinal contents enter the rectum, mechanoreceptors in the intestinal walls register increased tension in the intestinal wall. Mechanoreceptors, or stretch receptors, are sensory cells of the sense of touch found in every skin and mucosal surface and correspond to the first instance of pressure and touch sensations. As soon as the receptors in the intestinal wall register the increase in pressure, they convert it into a bioelectrical excitation and send it on to the brain via afferent nerve pathways, where the information passes into consciousness. When this happens, the person perceives a so-called urge to defecate. Depending on the period of time during which defecation is suppressed, the rectum adapts to a greater or lesser filling volume. As soon as defecation can no longer be suppressed, we speak of an imperative urge to defecate. Control over defecation is learned and does not exist from birth. Thus, as soon as the stretch receptors of young children report a stretch, the bowel empties itself, thus shortening the time span of the urge to defecate to a few seconds.

Function and task

Through the physiological process of defecation, the human rectum empties itself and disposes of indigestible food residues in this way. Adult humans generally have control over their defecation, which is described by the term continence. For defecation, a propulsive mass movement takes place in the intestine, mainly involving the far oral segments of the intestine. These movements occur after a meal and are then called gastrocolic reflex. The anus closes the rectum, into which the digested intestinal contents enter through the intestinal movements. Mechanoreceptors regsitrate an increase in wall tension as the digested intestinal contents enter the rectum and are excited by this stretch. They convert the stimuli into a proportional action potential, which they send to the posterior cord pathways of the spinal cord via viscerosensitive afferent nerve pathways called the nervi splanchnici pelvici. From the spinal cord, the signals travel to the somatosensory cortex of the brain. As the rectum fills, the sphincter ani internus muscle dilates in a reflex response. The fact that humans can still prevent involuntary defecation is due to the voluntary innervated sphincter ani externus muscle. This muscle remains contracted even after the first urge to defecate and thus maintains continence. The totality of the situation described is perceived by the human as an urge to defecate. Depending on how long the urge to defecate is suppressed, the sphincter ani internus muscle contracts and the rectum adapts to the increasing filling volume in the rectum. Only during defecation do both muscles of the anus become flaccid. The puborectalis muscle also no longer contracts. The corpus cavernosum recti swells at the same time. The rectosigmoid contracts reflexly and drives the emptying of the bowel contents from the sides of the oral bowel segments. When the rectum is appropriately full, the anus opens automatically as soon as the affected person squats.

Diseases and complaints

A pathological special form of defecation urge is severe types of imperative defecation urge. Such complaints may accompany intestinal diseases such as ulcerative colitis, and they are usually symptoms of particularly advanced stages of the disease. In the case of an extremely imperative urge to defecate, the affected person is often unable to hold the stool once the urge to defecate sets in. Holding out or pushing away is not possible for the affected person. They must visit the toilet immediately after the onset of the urge to defecate. Extremely imperative defecation urges considerably restrict the daily life of those affected, but fortunately they can be treated.In principle, a bowel movement should not be postponed for too long after the onset of the urge to defecate, as otherwise discomfort may develop during defecation. However, bowel movements should likewise not be approached prematurely and caused by extreme pressing. For some people, the feeling of urgency persists even though they have just relieved themselves. In such cases, light pressing can give the digested stomach contents an additional push. However, when there is no longer enough stool in the rectum, the automatic anal opening for defecation may not be triggered. In such a case, toileting should be stopped prematurely. No defecation should take more than a few minutes. If the urge to defecate persists even though defecation is no longer possible due to the filling volume in the rectum, these complaints often have pathollogical value. In most cases, persistent urge to defecate is related to hemorrhoids, which often encourage the patient to continue pressing. However, this approach often causes additional enlargement of the hemorrhoids. Thus, stool regulation problems and exaggerated pressing movements during defecation are among the most common causes of enlarged hemorrhoids. Therefore, the phenomenon should be treated, for example, with medication and discussed with a doctor.