Defecation is the emptying of the rectum and thus the disposal of indigestible components of food. Defecation is also called bowel movement.
What is defecation?
Defecation is the emptying of the rectum and thus the disposal of indigestible components of food. Feces, also called feces, consists of indigestible food components such as dietary fiber, undigested remnants of fats and starches, connective tissue and muscle fibers, and mostly water. Excreted intestinal cells, mucus and digestive enzymes are also contained in the feces. The feces obtain their coloration from the pigment stercobilin. The feces are formed during digestion in the intestine. There it is mixed and transported further until it is finally collected in the rectum. Stretch receptors in the intestinal wall signal when emptying is necessary. The need to visit a toilet then arises. Normally, defecation can be consciously controlled by the person. If this is no longer the case, we speak of incontinence. Disturbances in defecation are referred to as dyschezia.
Function and task
The amount of feces produced and excreted per day varies from person to person as well as from day to day. How much feces is excreted depends in large part on diet. Amounts of 100 to 500 grams per day are considered normal. If the diet is high in fiber, for example in vegetarians, the amount of feces can still exceed the upper limit of 500 grams. The frequency of defecation in healthy people varies between three times a day and three times a week. The consistency of the stool also varies between soft and hard. The beginning of defecation is in the large intestine or quite possibly in parts of the upper digestive tract. When food is ingested, stretch receptors in the mouth, esophagus and parts of the stomach are excited. The excited receptors transmit the information about food intake to the large intestine. The colon then reacts with strong contractions. The resulting peristaltic, i.e. undulating, movements of the intestinal muscles transport the contents of the large intestine further in the direction of the rectum. In this way, the colon tries to make room for the announced food. This reaction is also called the gastrocolic reflex. The rectum is closed by the intestinal outlet, the so-called anus. Thus, feces passed from the colon are first collected in the rectum. This increases the wall tension of the rectal wall. The stretch receptors in the wall of the rectum are then excited and send electrical signals to the brain via special nerve pathways, the viscerosensitive afferents. The sensory cortex is responsible for defecation. Now the need to defecate is stimulated for the first time. The filling of the rectum also causes the sphincter ani internus muscle to dilate. This internal anal sphincter cannot be controlled voluntarily and is intended to prevent involuntary defecation. If this muscle dilates, this is perceived as an urge to defecate. The discharge of stool is still prevented by the external anal sphincter. This can be controlled voluntarily up to a certain filling level of the rectum. During defecation, both sphincters relax and the puborectalis muscle, a muscle of the pelvic floor musculature, also relaxes. The cavernous body in the region of the anus (corpus cavernosum recti) swells and at the same time there is a reflex tightening of the posterior colon. This pushes the stool further toward the anus until it is finally expelled. Defecation can be assisted by muscular abdominal press.
Diseases and complaints
A common defecation disorder is constipation. Constipation is said to occur when defecation is difficult, less than three times a week, or incomplete. Around a quarter of the German population suffers from constipation. The risk of defecation disorders increases with age. Two forms are distinguished in chronic constipation. In slow-transit constipation, there is a transport disorder in the intestine. Those affected have virtually no spontaneous bowel movements and suffer from a feeling of fullness. The abdomen is very distended. Younger women in particular are affected. The causes are not yet fully understood. Nerve disorders, medications, sociological and psychological factors are under discussion as causes.The other form of constipation is called outlet obstruction or obstructive defecation syndrome. In this case, there is a defecation disorder of the rectum. This means that although patients feel an urge to defecate, the stool can only be emptied incompletely and in small portions. This defecation blockage is accompanied by pain in the rectal area. In some cases, those affected have to support defecation by applying pressure with the hand to the perineum or vagina, or even manually clear out the rectum. Here, too, sociological and psychological factors are suspected as triggers in addition to organic ones. Defecation disorders can also be caused by disturbances in the hormonal system, for example, by an underactive thyroid gland or diabetes mellitus. Neurological diseases such as multiple sclerosis or depression, as well as metabolic diseases, also negatively affect defecation. The loss of control over excretion of stool is called fecal incontinence. This can be due to various causes. Changed stool consistency, for example, in chronic inflammatory bowel diseases or diarrhea caused by infections can cause (temporary) fecal incontinence. Involuntary excretion of stool can also occur in the event of an obstruction of the rectum, i.e. an artificial bowel outlet, caused for example by a tumor. Other conceivable causes include dementia, defects in the sphincter muscles, pelvic floor disorders, or local inflammation of the anus.
