2013-02-08 Physio GI Hormones Flashcards
What are the two major families of the gut hormones? Which hormones fall into each?
gastrin family
- gastrin
- cholecystokinin (CCK)
- motilin
- enkephalin
secretin family
- secretin
- vasoactive intestinal polypeptide (VIP)
- gastric inhibitory polypeptide (GIP)
- pancreatic glucagon
- gut glucagon-like immunoreactivity (GLP-1)
- Bombesin (a.k.a. gastrin releasing peptide, GRP)
- vagal transmitter: release of gastrin following vagal stimulation.
How is the gut innervated?
Two systems:
intrinsic system has two plexuses:
- lumen
- mucosa
- Meissner in mucosa
- circ SMM
- **Auerbach **between SMM layers
- longit SMM
- serosa
- extrinsic parasympathetic, pre-ganglionic neurons synapse here
- gut has more neurons than the brain!
extrinsic system
- parasympathetic—pre-synaptic fibers synapse w/ intrinsic neurons
- sympathetic—post-synaptic fibers directly innervate
- parasympathetic—pre-synaptic fibers synapse w/ intrinsic neurons
What are the effects of gastrin?
stimulates acid secretion from parietal (oxyntic) cells of stomach (acting w/ histamine and ACh)
indirectly incr pepesinogen release from the chief cells
encourages growth of stomach mucosa (trophic effect)
- allows you to make even more HCl
stimulates gut motility
What are the effects of CCK?
- Stimulates:
- pancreatic HCO3- secretion
- pancr. enzyme secretetion
- gallbladder contraction
What are the effects of secretin?
Stimulates:
- Pancreatic HCO3- secretion
- Bile HCO3- secretion
ADD MORE
Describe the structural homology between members of the gastrin/CCK family?
Similar C-termini (5 aa’s same; C-termini are aminated)
- can give just that terminal 5 aa chain (pentagastrin) clinically
Vary in position and sulfonation of Tyrsoine residue
- sulfonation increases activity
What are the different sizes of gastrin? When are they secreted?
Big = 34aa—majority of what is secreted by antrum of stomach after a meal; degraded quickly
Little = 17aa—majority of what is found in the bloodstream
Mini = 14aa
How is gastrin release regulated?
Release is stimulated by:
- peptides in the chyme
- amino acids in the chyme
- vagal activity via bombesin=GRP (gastrin-releasing peptide)
- can be due to taste/scent! cool!
- calcium in the chyme [TUMS =(]
Release is inhibited by:
- pH falling <3.5 indirectly via paracrine action of somatostatin (see image)
Where is gastrin made?
G-cells in the antrum of the stomach and the proximal small gut
What are the chief actions of CCK?
Main action is on the pancreas
- stims pancr. proenz/enz release
- stims gallbladder contraction—>incr bile flow
- relaxes Sphincter of Oddi
- sphincer of Vater’s ampulla (jct of common bile duct w/ duodenum)
- reduces gastrin-induced acid secretion via compet. inhib.
- acts synergisticaly with secretin to incr pancr HCO3 release
How is CCK release controlled?
peptides and aa’s in the chyme are major stimulus of CCK release
fats and acidity are also weak stimuators
Where is CCK made?
CCK is synthesized by I-cells in the mucosal epithelium of the small intestine and secreted in the duodenum (Wikipedia)
What are the chief actions of secretin?
MAJOR PURPOSE: stimulates pancr. HCO3 secretion into duodenum (synergistic w/ CCK)
- inhibs HCl secretion in stomach—>by inhib’ing gastrin release
- acts synergistically w/ CCK on: release of pancr. enzymes and bile flow
What makes secretin?
Secretin is made by S-cells of the duodenum, which are located in the crypts of Lieberkühn
What controls secretin release?
Secretin is release in response to acid (pH<4) being introduced into the proximal small gut
