GI: Physiology Flashcards
What two neurologic plexuses lie within the GI tract and form the intrinsic nervous system? Where are they located?
Submucosal plexus: between the submucosa and the circular muscle layer
Myenteric plexus: between the circular muscle and longitudinal muscle
Postganglionic neurons of the parasympathetic nervous system have two classifications based on the neurotransmitter produced. Name them
Cholingergic: release acetylcholine
Peptidergic: release peptides such as substance P and vasoactive inhibitory peptide (VIP)
Name 3 effects of acetylcholine (parasympathetic stimulation) on the GI tract
Contraction of smooth muscle, relaxation of sphincters, increased secretion (salivary, gastric, and pancreatic)
Name 3 effects of norepinephrine (sympathetic stimulation) on the GI tract
Relaxation of smooth muscle, contraction of sphincters, increased salivary secretion
Name 2 effects of vasoactive intestinal peptide (VIP) on the GI tract
Relaxation of smooth muscle sphincters (receptive relaxation in the stomach, increased intestinal and pancreatic secretion
Name 2 effects of neuropeptide Y on the GI tract
Relaxation of smooth muscle (inhibits motility), decreased intestinal secretion
Name 2 effects of substance P on the GI tract
Secreted with parasympathetic stimulation: contraction of smooth muscle, increased salivary secretion
Name 4 gastrointestinal hormones:
Gastrin, cholecystokinin, secretin, GIP
Where is gastrin produced?
G cells in the antrum of the stomach
What stimulates gastrin secretion?
Ingestion of protein (small peptides, amino acids - phenylalanine and tryptophan most effective), distention of the stomach, vagal stimulation (gastrin releasing peptide)
Name 2 effects of gastrin
- Increases H+ secretion by the parietal cells
- Stimulates growth of the gastric mucosa
What inhibits gastrin secretion?
Low pH of gastric contents, somatostatin
What cells produce cholecystokinin (CCK)?
I cells of the duodenal and jejunal mucosa
What stimulates CCK production?
- Monoglycerides and fatty acids (NOT triglycerides)
- Small peptides and amino acids
Name the 5 actions of CCK
- Contraction of the gallbladder/relaxation of the sphincter of Oddi to eject bile
- Secretion of pancreatic enzymes
- Secretion of bicarbonate from the pancreas
- Growth of the exocrine pancreas and gallbladder
- Inhibition of gastric emptying
What cells produce secretin?
S cells of the duodenum
What stimulates secretion production?
H+ and fatty acids in the lumen of the small intestine
What is the function of secretin?
- Promote secretion of pancreatic and biliary HCO3- to neutralize stomach acid
- Inhibits effects of gastrin on parietal cells
Glucose-dependent insulinotropic peptide (GIP) is secreted by what cells?
K cells of the duodenal and jejunal mucosa
What stimulates GIP secretion?
All 3 major nutrients: glucose, amino acids, fatty acids
What is the effect of GIP?
- Stimulation of insulin secretion by the pancreatic beta cells
- Inhibition of gastric H+ secretion
- Slows gastric emptying
- Stimulates lipogenesis
Where is motilin secreted and what does it do?
- Secreted from the upper duodenum during fasting states by M cells
- Regulates interdigestive myoelectric complexes