6. Physiology of the GI DSA Flashcards
What is the function of gastrin?
Increases H+ secretion by the parietal cells
Stimulates the growth of the gastric mucosa
Does the enteric nervous system require CNS input, or can it function independently?
The enteric nervous system can exert its functions without CNS input.
What five neurotransmitters (in the final table of the DSA) are secreted by neurons of the enteric nervous system?
Vasoactive intestinal peptide (VIP).
Nitric oxide.
Enkephalins.
Neuropeptide Y.
Substance P.
What receptor is used between pre-and postganglionic cells?
Nicotinic acetylcholine receptors
What is the main goal of secretin?
What are the functions of secretin to accomplish this goal?
Secretin’s goal is to increase the pH of the gastric contents in the duodenum to between 6 and 8 to allow for pancreatic lipase function.
Secretin increases pancreatic and biliary HCO3- secretion, and inhibits gastrin (both the H+ production effect and the trophic effect) to accomplish this.
What is the function of nitric oxide on the G.I.?
Relaxation of smooth muscle.
What is the main function of glucose-dependent insulinotropic peptide (GIP)?
What are the secondary functions?
GIP increases insulin production from the beta cells of the pancreas.
GIP also inhibits gastric H+ production, and delays gastric emptying (like cholecystokinin).
What is the function of somatostatin?
Response to decreased pH in the lumen, and inhibits other G.I. hormones as well as gastric H+ secretion.
Why would oral glucose administration increase insulin secretion more effectively than intravenous glucose administration?
Because of the action of incretins like GIP.
What are the actions of norepinephrine on the G.I.?
Relaxes the smooth muscle of the intestinal wall, but contracts sphincters. (Opposite of acetylcholine).
Increases salivary secretion.
Where is somatostatin secreted outside of the G.I. tract?
In the Delta cells of the endocrine pancreas and by the hypothalamus
What are the functions of substance P on the G.I.?
Contraction of smooth muscle (like enkephalins).
Increased salivary excretion.
What stimulates cholecystokinin release?
Monoacylglycerols, fatty acids, small peptides, amino acids.
What cells of the G.I. tract secrete somatostatin?
The D cells of the G.I. mucosa
What are the five actions of cholecystokinin?
Contraction of the gallbladder and relaxation of the sphincter of Oddi.
A trophic (growth) effect on the exocrine pancreas and gallbladder.
Secretion of pancreatic enzymes (lipase, amylase, and protease).
Potentiates the effect of secretin on bicarbonate secretion by the pancreas.
Inhibits gastric emptying to increase gastric emptying time for digestion of fats.
By which cells is gastrin released?
The G cells of the stomach
What is the function of gastrin releasing peptide (GRP) on the G.I.?
What is the source of GRP?
GRP increases gastrin secretion.
GRP is released by the vagal neurons of the gastric mucosa.
What is the action of vasoactive intestinal peptide (VIP) on the G.I.?
Relaxation of smooth muscle.
Increased intestinal secretion.
Increased pancreatic secretion.
What neurotransmitter is released by the postganglionic nerve fibers of the sympathetic nervous system in the G.I.?
Norepinephrine
What is the function of enterochromaffin-like cells?
Storage and production of histamine, to increase H+ secretion by the parietal cells
What are the functions of enkephalins on the G.I.?
Contraction of smooth muscle.
Decreased intestinal secretion.
What are the functions of neuropeptide Y on the G.I.?
Relaxation of smooth muscle.
Decreased intestinal secretion.
How is substance P secreted?
It is co-secreted with acetylcholine (by enteric nervous system neurons).
What three things stimulates the release of gastrin?
Distention of the stomach
Stimulation by the vagus nerve
Presence of small peptides and amino acids
Where is cholecystokinin released?
From the I cells of the duodenal and jejunal mucosa.
What two nerves serve as the parasympathetic innervation of the G.I.?
The vagus and pelvic nerves
What are the actions of acetylcholine on the G.I.?
Contracts smooth muscle of the intestinal wall, but relaxes sphincters. (Opposite of norepinephrine).
Increases salivary secretion.
Increases gastric secretion.
Increases pancreatic secretion.
