Gastrocolic reflex
Encyclopedia
The gastrocolic reflex or gastrocolic response is one of a number of physiological reflexes controlling the motility
, or peristalsis
, of the gastrointestinal tract
. It involves an increase in motility of the colon
in response to stretch in the stomach
and byproducts of digestion in the small intestine
. Thus, this reflex is responsible for the urge to defecate following a meal. The small intestine also shows a similar motility response. The gastrocolic reflex helps make room for more food.
The reflex was demonstrated by myoelectric recordings in the colons of animals and humans, which showed an increase in electrical activity within as little as 15 minutes after eating. The recordings also demonstrated that the gastrocolic reflex is uneven in its distribution throughout the colon. The sigmoid colon
is more greatly affected than the right side of the colon in terms of a phasic response; however, the tonic response across the colon is uncertain. When pressure within the rectum becomes increased, the gastrocolic reflex acts as a stimulus for defecation. A number of neuropeptides have been proposed as mediators of the gastrocolic reflex. These include serotonin
, neurotensin
, cholecystokinin
(CCK), and gastrin
.
Clinically, the gastrocolic reflex has been implicated in pathogenesis of irritable bowel syndrome
: the very act of eating or drinking can provoke an overreaction of the gastrocolic response in some patients with irritable bowel syndrome due to their heightened visceral sensitivity, and this can lead to abdominal pain, diarrhea, or constipation. Also, the serotonin (5HT3) antagonist ondansetron
decreases the tonic response to stretch.
Motility
Motility is a biological term which refers to the ability to move spontaneously and actively, consuming energy in the process. Most animals are motile but the term applies to single-celled and simple multicellular organisms, as well as to some mechanisms of fluid flow in multicellular organs, in...
, or peristalsis
Peristalsis
Peristalsis is a radially symmetrical contraction and relaxation of muscles which propagates in a wave down the muscular tube, in an anterograde fashion. In humans, peristalsis is found in the contraction of smooth muscles to propel contents through the digestive tract. Earthworms use a similar...
, of the gastrointestinal tract
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
. It involves an increase in motility of the colon
Colon (anatomy)
The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...
in response to stretch in the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
and byproducts of digestion in the small intestine
Small intestine
The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
. Thus, this reflex is responsible for the urge to defecate following a meal. The small intestine also shows a similar motility response. The gastrocolic reflex helps make room for more food.
The reflex was demonstrated by myoelectric recordings in the colons of animals and humans, which showed an increase in electrical activity within as little as 15 minutes after eating. The recordings also demonstrated that the gastrocolic reflex is uneven in its distribution throughout the colon. The sigmoid colon
Sigmoid colon
The sigmoid colon is the part of the large intestine that is closest to the rectum and anus. It forms a loop that averages about 40 cm...
is more greatly affected than the right side of the colon in terms of a phasic response; however, the tonic response across the colon is uncertain. When pressure within the rectum becomes increased, the gastrocolic reflex acts as a stimulus for defecation. A number of neuropeptides have been proposed as mediators of the gastrocolic reflex. These include serotonin
Serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
, neurotensin
Neurotensin
Neurotensin is a 13 amino acid neuropeptide that is implicated in the regulation of luteinizing hormone and prolactin release and has significant interaction with the dopaminergic system...
, cholecystokinin
Cholecystokinin
Cholecystokinin is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein...
(CCK), and gastrin
Gastrin
In humans, gastrin is a peptide hormone that stimulates secretion of gastric acid by the parietal cells of the stomach and aids in gastric motility. It is released by G cells in the antrum of the stomach, duodenum, and the pancreas...
.
Clinically, the gastrocolic reflex has been implicated in pathogenesis of irritable bowel syndrome
Irritable bowel syndrome
Irritable bowel syndrome is a diagnosis of exclusion. It is a functional bowel disorder characterized by chronic abdominal pain, discomfort, bloating, and alteration of bowel habits in the absence of any detectable organic cause. In some cases, the symptoms are relieved by bowel movements...
: the very act of eating or drinking can provoke an overreaction of the gastrocolic response in some patients with irritable bowel syndrome due to their heightened visceral sensitivity, and this can lead to abdominal pain, diarrhea, or constipation. Also, the serotonin (5HT3) antagonist ondansetron
Ondansetron
Ondansetron is a serotonin 5-HT3 receptor antagonist used mainly as an antiemetic , often following chemotherapy. Its effects are thought to be on both peripheral and central nerves...
decreases the tonic response to stretch.