Muscle activity and the resulting movements of hollow organs are called peristalsis. The Intestinal peristalsis serves primarily to mix the chyme and its forwarding towards the rectum or anus. The term intestinal peristalsis is sometimes used synonymously with terms such as bowel movements or bowel motility. However, intestinal peristalsis actually only includes propulsive and non-propulsive peristalsis. All other bowel movements fall under the term bowel motility.
What is intestinal peristalsis?
A movement pattern of hollow organs that results from the synchronous activity of the cells of the smooth muscles is called peristalsis. Typical peristalsis run in waves with alternating phases of contraction and relaxation of the muscles.
The intestinal peristalsis is based on the contraction and relaxation of the longitudinal and circular muscles of the intestine. It is found throughout the intestine, that is, both in the sections of the small intestine and in the large intestine.
The casing has a special wall structure for this function. The innermost layer of the intestinal wall is the tunica mucosa, a layer of the mucous membrane. On top of this lies a muscle layer, consisting of a circular muscle layer (stratum circulare or stratum annulare) and a longitudinal muscle layer (stratum longitudinal). The outermost intestinal layer is called the tunica adventitia. The special intestinal peristalsis is only possible through the longitudinal and circular muscles.
Function & task
In the intestine, a distinction can be made between propulsive and non-propulsive intestinal peristalsis. The non-propulsive peristalsis arises from ring-shaped, locally occurring contraction waves and is also known as segmentation. Its main purpose is to mix the chyme in the intestine.
In propulsive peristalsis, the ring-shaped muscles also contract, but the movement is continued with the involvement of the longitudinal muscles. One speaks here of a tonic permanent contraction of the intestinal muscles. The propulsive peristalsis serves to transport the chyme towards the anus.
In addition to these two forms of intestinal peristalsis, a differentiation can be made between retrograde and orthograde peristalsis. With orthograde peristalsis, the intestinal contents are transported in the right direction, i.e. towards the rectum. In retrograde peristalsis, the direction of transport is reversed. This condition can be surgically created in humans to slow down the passage time of the chyme through the intestines.
The control of the intestinal peristalsis is subject to the so-called pacemaker cells. They set the rhythm of the peristalsis. The pacemaker cells in the smooth muscle of the gastrointestinal tract are also called interstitial Cajal cells (ICC). These are spindle-shaped cells that are located in the longitudinal muscle layer of the intestine. They act as a kind of mediator between the muscle cells and the excitatory and inhibitory nerve cells of the intestine.
There is another group of Cajal cells in the intestinal muscles. These form a branched connection between the longitudinal and the circular muscles and form the actual pacemaker. They are closely related to the so-called Auerbach plexus. The Auerbach plexus is a network of nerves in the intestinal wall and is responsible for the intestinal peristalsis and, in particular, for controlling the contractions of the smooth muscle cells. The pacemaker cells in turn are subject to the control of the autonomic nervous system. The muscles also have a certain rhythm of their own, but increased peristalsis may be necessary depending on the food intake.
The peristaltic reflex is responsible for an increased intestinal peristalsis after eating. Inside the stomach wall and intestinal wall are mechanoreceptors that respond to stretching. If the stomach or intestines are stretched by the ingested food, the cells of the enteric nervous system release serotonin. This stimulates other nerve cells in the intestinal wall, including the pacemaker cells. These in turn cause the muscle contractions of the intestinal muscle cells.
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Disturbances of the intestinal peristalsis can occur in various diseases. In the case of paralytic ileus, a form of intestinal obstruction, the peristalsis comes to a complete standstill due to a functional disorder, so that ultimately there is intestinal paralysis. The intestinal passage is interrupted and there is a build-up of porridge and feces in the intestine.
The most common trigger of a paralytic ileus is an inflammation in the abdominal cavity such as appendicitis, gallbladder inflammation or pancreatitis. Vascular occlusions, pregnancy or various drugs such as opiates, antidepressants and drugs for Parkinson's disease can also result in paralytic ileus.
While the intestinal peristalsis comes to a complete standstill in paralytic ileus, it is sometimes even increased in mechanical ileus. In the case of mechanical ileus, the passage of the intestine is prevented by a mechanical obstacle inside the intestine. A mechanical ileus can be caused by balls of feces, foreign bodies, gallstones, entrapment or intestinal entanglement.
Mechanical ileus can also occur as a complication of an umbilical or inguinal hernia. In the case of a mechanical ileus, the intestine tries to transport the chyme past the closure more intensely. Therefore, the peristalsis is increased in the bowel section in front of the obstruction.
Typical symptoms of an intestinal obstruction are vomiting, possibly even vomiting of excrement, flatulence within the intestine and complete stool and wind retention. An ileus can seriously damage the intestinal wall, so that bacteria from the intestine can enter the abdominal cavity and cause a life-threatening inflammation of the peritoneum there.
In irritable bowel syndrome, the intestinal peristalsis is almost always disturbed. Irritable bowel syndrome is the most common intestinal disorder. It is a chronic dysfunction with an unknown cause. The symptoms of irritable bowel syndrome are very diverse. The disturbed peristalsis leads to diarrhea alternating with constipation, stomach pain, a feeling of fullness and bloating. Defecation is often painful. The patient's condition worsens, especially in stressful situations. Some doctors therefore count irritable bowel syndrome among the psychosomatic diseases.
