Exam 3 Review:  Chapter 23:  Regulation of Digestion

gastrin - A peptide hormone, secreted in response to gastric distension or a rise in gastric pH by enteroendocrine cells (G cells) within the glandular pits in the mucous membrane of the stomach, which stimulates the production of HCl by parietal cells; an important regulator of stomach digestive processes during the middle gastric phase; it also promotes gastric mucosal growth.

gastric inhibitory peptide = GIP - A peptide hormone, secreted in response to duodenal distension or the detection of glucose and fatty acids in the chyme arriving from the stomach; it is secreted by enteroendocrine cells beneath the mucosal epithelial cells of the duodenum; it stimulates the release on insulin from beta cells of the pancreatic islets and inhibits the release of gastric HCl from the parietal cells and pepsin from the chief cells of the gastric mucosa.

secretin - A peptide hormone, secreted in response to the detection of gastric HCl in the chyme arriving from the stomach; it is secreted by enteroendocrine cells from the mucosal epithelium cells of the duodenum; it stimulates the production of bicarbonate-rich alkaline secretion from pancreatic ductal cells, and, to a lesser degree, from bile duct cells.

cholecystokinin = CCK - A peptide hormone produced principally by the enteroendocrine cells from the mucosal epithelium of the duodenum in response to the presence of  fatty acids and proteins in the chyme arriving from the stomach; it stimulates the contraction of the gallbladder, release of bile, and secretion of pancreatic digestive enzymes from the pancreatic acinar cells.  aka - pancreozymin (older terminology).  [Note:  It is also found in the CNS and may be related to the control of feelings of satiety (fullness, lack of hunger).]

enterogastric reflex - One of the visceral = autonomic reflexes involved in the regulation of digestion in which sensory signals from distension of the small intestine and the detection of gastric HCl in the chyme inhibit gastric motility and gastric secretion; it also encourages secretion of bile from the gall bladder and pancreatic juice from the pancreas; it is mediated by parasympathetic autonomic motor impulses.

gastric emptying - The passage of the contents of the stomach into the small intestine; it is influenced by the content of the meal, by hyperglycemia, by digestive hormone (gastrin, cholecystokinin, vasoactive intestinal polypeptide and gastric inhibitory peptide) levels, and regulatory impulses from the ANS; solid foods generally require approximately 90 minutes/half-time while liquids move faster.

distension - The act or process of expanding or stretching a structure by pressure from within, e.g., by filling the structure with material.   

Describe:

1. the hormones secreted by the duodenum and how they regulate secretion by the stomach (gastric), liver (hepatic), gall bladder (cystic), and pancreas (pancreatic).

2. how gastric emptying is regulated.

Autonomic NS Regulation:  Increased sympathetic impulses and decreased parasympathetic impulses to gastric smooth muscle stimulate emptying.  Duodenal proprioceptive stretch recepters provide negative feedback information to inhibit emptying if the duodenum becomes overfilled.

Chemicals (free fatty acids, hydrogen ions, electrolytes) in the duodenal chyme stimulate the release of secretin, cholecystokinin (CCK) and gastric inhibitory peptide (GIP), all of which inhibit the rate of emptying.