L7 funcs of the stomach

Question 1

LO4: expl mechs of stom ac sec.

Answer 1

-gastric pit and gl. gastric pit bef meck, surf mucous cells. mucous neck cells. gastric gl below neck. parietal cells, chrief cells, enteroendoc cells, G+D. in that order.

Question 2

LO1: desc funcs of stom.
LO2: desc patts motil incl recep relax and peristal.
LO3: desc compons of gastric sec and cell ori.

Answer 2

-RECEIVE AND STOR FOOD:
recep relax- vagally med relax orad, prev high intragastric press. rugae distens. bod basal tone.
-DISRUP FOOD:
stom larger proxim acts as funnel, food accel down, large left beh. antrum and pyloris musc. pyloris small, propell tow then refl back. chyme squirt 3x min. peristal mixes stom cont. contrac ev 20 sec proxim to distal.
-CONTIN DIG:
acid conds unrav prot and activ protease eg pepsinogen to pepsin catal by hcl. disinfec. ph under 2. 100mM HCL.
parietal cell most fundus and bod- prod HCl and intrinsic fac- abs vitB12, lack=pernic anaemia with large BCs.
G cells main antrum- gastrin.
enterochromaffin like cells (ECL)- histamine. regs stom ac.
chief- pepsinogen percurs.
D cell- somatostatin neg feedb on ac prod.
mucous cells surf and neck- mucus for protec.
-stom secs mucus, HCO3, HCl, pepsinogen.

Question 3

LO5: expl contr of stom ac sec.

Answer 3

-HCl sec contr- parietal STIM by gastrin, histam, Ach. diverse contr allow var deg prod, combin synerg. vagus nerve=Ach=McR. Ach from post gang PS nerves, stim by distens. ECL=histam=H2R. blood gastrin= CCKR to H+ pump.
- gastrin sec contr- G cell STIM by pep/aa in stom lumen as G cell x mem. vagal stim Ach and gastrin rel pep bind its R. INHIB by somatostatin.
-HCl INHIB- essen inhib of g cells. food leave stom= decr pH transient. food is buff. low pH=activ D cells= rel somatostat= inhib G and ECL, block H2 and CCKRs.
-HCl prod- water split in pariet mito. H+ to stom lumen by H+ pump in wall of canaliculi-invag lumin pariet. cl to stom from ECF, exch for HCO3- 1 mol for 1 mol. form HCl.
CO2 comb OH- form HCO3- by carbinic anhydrase. into blood= alk tide. re sec by panc and liver to neut chyme. H+ pump req lot atp.
-phases dig:
cephalic- 30% tot HCl. neural contr. prep bef food. smell/taste/chew/swall. dir stim pariet by vagus. stim G cells by vagus (GRP rel).
gastric- 60%. stom distens stim vagus-stims pariet and G. aa and small pep stim G. food buff-rem inhib on gastrin prod. ph incr switch off D cells so cant inhib proc via somatostat.
intestinal- 10% duod. chyme init stim gastrin sec. short phase. soon inhib of G take over. chyme leave= cholecytokinin and GIP rel= decr ac sec.

Question 4

LO6: desc func of stom defs.

Answer 4

• mucus and HCO3-. surf mucus cells and neck cells in gastric gl. forms thick alk viscous lay adheres epith. insul ph. high turnover epith keeps intact. prostaglandins maint mucosal blood flow- supp epith mutr for renew and rep. stim prod of defs.
• breach defs- alc diss mucus. H pylori chromic gastritis. NSAIDS inhib prostaglandins prev blood flow. leads to- gastritis, ulcerat, reflux dis.

Question 5

LO7: outl how gastric ac sec decr by drugs.

Answer 5

• can do vagotomy. trunk and branches many funcs. dont do trunk anym. selective vagotomy smaller br but need leave drain in pylor sphinct as cant relax. now highly selec vagotomys br that stims pariet cells.
• H2 blocker prev histam activ pariet. eg cimetidine, ranitidine.
• H+ pump inhib eg omeprazole.

Question 6

LO8: desc proc gastric emp and its contr.

Answer 6

-squirt chyme ev perist wave, pyloris shut btw. emp rate contr by feedb from duod by chem sigs so approp for furth dis and abs. fats slow gastric emp as take more time to dig and abs.

Question 7

struc and func.

Answer 7

-when empty gastric canal temp btw lesser curve folds= saliv and fluid and some food pass.
-gastric mucosa 3 zone: cardia- mucus sec gls mostly. fundus- gastric gl consis of mucus sec neck cells, pariet cells, chief and other. horm prod cell (APUD). pyloric reg- gls sec mucus and gastrin.
-gastric ulcers comm antrum and lesser curve. perfor ulcer= spill to perit cav aff eg panc and BV.
-freq reflux/insuff clearabce= heartburn and/or inflamm with ulcerat. chromic can= metaplastic alt in mucosa= barrtetts oesoph incr risk carcinoma. alc and smok incr CA. comm lower oesoph. can=dysphag.
gastritis acute eg NSAIDS/alc=exfol epith decr muc sec. chronic H pylori=inflamm mucosa=atrophy and metaplasia.