The endocrine system controls the function of the digestive system at various stages. Hormones that control the digestive function are gastrin, secretin, cholecystokinin, and gastric inhibitory peptide.
One of the important factors under hormonal control is the stomach acid environment. The hormone gastrin is secreted by G cells in the stomach in response to the presence of proteins. Gastrin stimulates the release of hydrochloric acid (HCl), which aids in the digestion of the majority of proteins. However, when the stomach is emptied, the acidic environment need not be maintained and a hormone called somatostatin stops the release of hydrochloric acid. This is controlled by a negative feedback mechanism.
In the duodenum, digestive secretions from the liver, pancreas, and gallbladder play an important role in digesting chyme during the intestinal phase. In order to neutralize the acidic chyme, a hormone called secretin stimulates the pancreas to produce alkaline bicarbonate solution and deliver it to the duodenum. Secretin acts with another hormone called cholecystokinin (CCK). Not only does CCK stimulate the pancreas to produce the requisite pancreatic juices, but it also stimulates the gallbladder to release bile into the duodenum.
Another level of hormonal control occurs in response to the composition of the food. Foods high in lipids (fatty foods) take a long time to digest. A hormone called gastric inhibitory peptide is secreted by the small intestine to slow down the peristaltic movements of the intestine to allow fatty foods more time to be digested and absorbed.
Practice Questions
https://jackwestin.com/khan-academy-mcat/helicobacter-pylori-and-the-gastrointestinal-system
Key Points
• Gastrin hormone is secreted in the stomach that stimulates the release of hydrochloric acid in the stomach.
• Secretin and cholecystokinin are secreted in the duodenum that helps in the production of alkaline bicarbonate in pancreatic juice that neutralizes the acidic contents that enter from the stomach in the duodenum.
• Gastric inhibitory peptide slows down the peristaltic movements of the intestine to allow fatty foods more time to be digested and absorbed.
Key Terms
chyme: partially digested food mixed with acidic gastric juice in the stomach
gastrin: a hormone that stimulates the secretion of gastric acid (HCl) by the parietal cells
g cell: a cell in the stomach and duodenum that secretes gastrin
somatostatin: is a growth-inhibiting hormone that regulates the endocrine system
negative feedback: occurs when some function of the output of a system, process, or mechanism is fed back in a manner that tends to reduce the fluctuations in the output
duodenum: the first part of the small intestine that starts at the lower end of the stomach and extending to the jejunum.
gall bladder: the small sac-shaped organ beneath the liver, in which bile is stored after secretion by the liver and before release into the intestine
secretin: a hormone that regulates water homeostasis throughout the body
cholecystokinin: a hormone which is secreted by cells in the duodenum and stimulates the release of bile into the intestine and the secretion of enzymes by the pancreas
bile: a fluid produced by the liver to digest the fats in the small intestine.
gastric inhibitory peptide: an inhibiting hormone stimulates insulin secretion and reduces peristalsis
peristalsis: contraction in the smooth muscle of the esophagus that helps in the transport of food
