GI secretion (#2) Flashcards
Which cells secrete acid in the stomach? Describe it.
Parietal cells;
1. HCl secreted from apical side that contains secretory canaliculus and proton pump.
Describe the parietal cell under resting conditions.
Tubulovesicles in cytoplasm; Canaliculus collapsed.
Describe the parietal cell when activated
Increased cAMP and Ca inserts the tubulovesicle into the membrane and secretes acid.
What are the 3 stimulants of acid secretion?
Ach, gastrin and histamine
What do enterochromaffin cells make?
5-HT and Histamine
How do muscarinic receptors on parietal cells work?
They couple to IP3 and increase intracellular calcium. Leads to insertion of HK ATPase in the membrane
How does prostaglandin work on parietal cells?
Couples to inhibition of adenylate cyclase and decrease in cAMP; Inhibits acid secretion.
How does prostaglandin work in gastric epithelial cells?
Stimulates mucous and bicarbonate secretion
Which drugs inhibit prostaglandin synthesis?
NSAIDS; Inhibit COX, causes ulcers and cytoprotectvie barrier
Which drugs are used to treat ulcers and GERD?
H2 antagonists; Cimetidine, ranitidine, nizatidine and famotidine
What are the 2 adverse effects of H2 antagonists?
Inhibits P450, anti-adrogenic effects
How do PPIs work?
- Require bioactivation via acidic pH in the stomach.
- Intermediates combine with sulfhydryl groups on enzyme deactivating it.
- Must make new enzyme.
Name some PPIs.
Omeprazole, Iansoprazole
When are PPIs used?
When H2 antagonists are ineffective.
What is Misoprotol?
An analog of prostagladin used to treat Peptic ulcer disease.
How does Colonic chloride secretion work?
- Pump transporter regulated by cAMP, PKA, DAG, and IP3
- Cell receptors are on basolateral surface.
- Ach works on muscarinic receptors which couple to DAG/PKC’ VIP couples to cAMP/PKA
How does sympathetics work on chloride secretion in the colon?
Pro-absorptive; Inhibits secretomotor neurons. NE acts on alpha-2 adrenergic receptors; Clonidine blocks this
How does Opiods affect colonic chloride secretion?
Inhibits Cl- transport via action at opiate receptor
How does lubiprostone affect colonic chloride secretion?
CIC-2 activator; Stimulates Cl- secretion and water movement into the lumen of the colon. Treats constipation
