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gihep 9: gastric function (ii) (proton pump (stimulated by... (Ach (binds…
gihep 9: gastric function (ii)
proton pump
H+/K+ ATPase
H+ from H2O into gastric lumen
K+ out of lumen into blood
needs energy
Cl- enters oxyntic cell + HCO3- leaves into blood
then CL- enters lumen down electrochem gradient
stimulated by...
Ach
binds to muscarinic Rs and IP3/DAG made via phospholipase C
Gastrin
Binds to CCKB and IP3/DAG made
histamine
binds to H2 R and cAMP made via adenylate cyclase
inhibited by PGE2 + somatostatin (inhibit adenylate cyclase)
H+ + Cl- in lumen = HCl
mediators of acid secretion
ACh increases all secretion + motility via GRP
gastrin + histamine release H2O + acid
acid activates pepsin
gastrin increases motility, relaxes pyloric sphincter contracts intestines, relaxes ileocaecal sphincter, stimulates mucosa proliferation
old view: ACh, gastrin + histamine = syngergistic
new view: histamine = main acid stimulant
absorption from stomach
small SA, no villi, tight junctions between epithelial cells
only highly lipid soluble agents absorbed here
aspirin, alcohol
causes of gastritis/ peptic ulcers
Zollinger-Ellison Syndrome
uncontrolled gastrin
pancreatic tumour
helicobacter pyloris
treatment = triple therapy
2 antibiotic + proton pump inhibitor
causes leukocyte infiltration + inflamm
most common
NSAID + steroids
inhibit PGE2
decreased mucus
aspirin + alcohol = irritants to mucosal barrier
excess acid/pepsin from reflux, stress,alcohol,caffeine,smoking