22.6C: Digestive Properties of the Stomach
The movement and flow of chemicals into the stomach is controlled by the autonomic nervous system and various digestive system hormones.
- List the various digestive properties of the stomach
Key Points
- Digestive hormones include: gastrin, somatostatin, cholecystokinin, secretin, gastric inhibitory peptide, and enteroglucagon.
- Gastrin causes an increase in the secretion of HCl from the parietal cells, an increase in pepsinogen from the chief cells in the stomach, and an increase in stomach motility.
- Somatostatin inhibits the activity of gastrin. Cholecystokinin (CCK) causes gall bladder contractions; it also decreases gastric emptying and increases the release of pancreatic juice that is alkaline and neutralizes the chyme. Secretin diminishes acid secretion in the stomach.
- Gastric inhibitory peptide (GIP) and enteroglucagon decrease gastric acid release and motility. They also turn off stomach action when the gall bladder and liver have not yet finished absorption.
- Epidermal growth factor (EGF), produced by the salivary glands, heals oral and gastroesophageal ulcers, inhibits gastric acid secretion, and stimulates DNA synthesis as well as mucosal protection.
- The stomach can sense, independently to the tongue and oral taste receptors, glucose, carbohydrates, proteins, fats, and sodium glutamate via the vagus nerve, which allows the brain to link the nutritional value of foods to their tastes.
Key Terms
- gastrin : A hormone that stimulates the production of gastric acid in the stomach.
- antrum : A bodily cavity, especially one having bony walls, especially in the sinuses.
- enteroglucagon : A peptide hormone derived from preproglucagon that is secreted from the mucosal cells, primarily of the colon and terminal ileum, that follows ingestion of a mixed meal to delay gastric emptying.
- somatostatin : A polypeptide hormone, secreted by the pancreas, that inhibits the production of certain other hormones.
EXAMPLES
Gastric ulcers can be healed by supplemental daily doses of epidermal growth factor (EGF). EGF inhibits bacterial colonization and speeds healing just as well as antibiotics.
Stomach Hormones
Fundic gland : The fundic gland, found in the stomach, secretes gastrin and other hormones.
The movement and the flow of chemicals into the stomach are controlled by both the autonomic nervous system and the various digestive system hormones.
The hormone gastrin causes an increase in the secretion of HCl from the parietal cells and pepsinogen from the chief cells in the stomach. It also causes increased motility (movement, peristalsis) in the stomach.
Gastrin is released by G-cells in the stomach, via the base cells of the pyloric, cardiac, and fundic glands, in response to distension of the antrum, and digestive products (especially large quantities of incompletely digested proteins). It is inhibited by a pH normally less than four (high acid), as well as the hormone somatostatin.
Cholecystokinin (CCK) primarily effects the gall bladder and causes it to contract, but it also decreases gastric emptying and increases release of pancreatic juice, which is alkaline and neutralizes the chyme.
In a different and rare manner, secretin that is produced in the small intestine primarily effects the pancreas, but it will also diminish acid secretion in the stomach. Gastric inhibitory peptide (GIP) decreases both gastric acid release and motility. Enteroglucagon decreases both gastric acid and motility.
Cardiac gland : The cardiac gland, found in the stomach, secretes gastrin and other hormones.
Other than gastrin, these hormones all act to turn off the stomach’s action. This is in response to food products in the liver and gall bladder that have not yet been absorbed. The stomach needs to push food into the small intestine only when it is not busy. While the intestine is full and still digesting food, the stomach will act as storage for food.
Epidermal Growth Factor
Epidermal growth factor (EGF) results in cellular proliferation, differentiation, and survival. EGF is a low-molecular-weight polypeptide that was first purified from a mouse’s submandibular gland, but has since been found in many human tissues including the submandibular and parotid glands.
Pyloric gland : The pyloric gland, found in the stomach, secretes gastrin and other hormones.
Salivary EGF, which seems to be regulated by dietary inorganic iodine, plays an important physiological role in the maintenance of oroesophageal and gastric tissue integrity. The biological effects of salivary EGF include the healing of oral and gastroesophageal ulcers, the inhibition of gastric acid secretion, and the stimulation of DNA synthesis, as well as providing mucosal protection from intraluminal injurious factors—such as gastric acid, bile acids, pepsin, and trypsin, and to physical, chemical, and bacterial agents.
The stomach can taste sodium glutamate using glutamate receptors. This information is passed to the lateral hypothalamus and limbic system in the brain as a palatability signal through the vagus nerve. The stomach can also sense, independently from the tongue and oral taste receptors, glucose, carbohydrates, proteins, and fats. This allows the brain to link the nutritional value of foods to their tastes.
Although absorption is the primary function of the small intestine, some absorption of certain small molecules does nevertheless occur in the stomach through its lining. This includes water if the body is too dehydrated; medication, like aspirin; and amino acids (e.g., whey protein shake).
There are many different gastric glands that secrete many different chemicals. Parietal cells secrete hydrochloric acid and intrinsic factor
- Chief cells secrete pepsinogen.
- Goblet cells secrete mucus.
- Argentaffin cells secrete serotonin and histamine.
- G cells secrete the hormone gastrin.
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