Gastric Acid Secretion Made Easy

Table of Contents

Steps for gastric acid secretion by parietal cells

1. H+ and HCO3- are produced from CO2 and H2O.

2. H+ is secreted into the lumen by H+/K+ ATPase pump.

3. HCO3- moves out of the cell, across the basolateral membrane via antiport with Cl-.

4. Cl- diffuses passively into the lumen via Cl- channel.

gastric acid secretion

Phases of Gastric Acid Secretion

PhasesAcid productionTriggerMechanismInhibition
1. Cephalic30%Psychic stimuliVagal stimulationLoss of appetite/Depression (lack of parasympathetic center stimulation)
2. Gastric60%Presence of food in stomach (mechanical and chemical)Distension: Vagovagal and local reflex

Chemical (high pH): G cells release Gastrin
Low PH: Gastrin secretion decreases

Emotional distress: Sympathetic stimulation
3. Intestinal10%Presence of food in duodenum (chemical)Chemical (low pH): Intestinal gastrin releasedDistension, Fatty acids, Hypertonic chyme:
a. Enterogastric reflex
b. Intestinal hormones (secretin, GIP, CCK, VIP)
Cholinergic stimulation and Gastrin both also stimulates Histamine secretion from ECL cells which in turn stimulates acid secretion.

Pharmacology

gastric acid pharmacology
Adam L. VanWert, Pharm.D., Ph.D., CC BY 3.0, via Wikimedia Commons

1. Reduction of gastric acid secretion: H2 antihistaminics, Proton pump inhibitors (PPI), M1 anticholinergics, PG analogs (EP3 receptor)

2. Neutralization of gastric acid: Antacids

3. Ulcer protectives: Sucralfate, Bismuth, PG analogs

4. Ulcer healing: Carbenoxolone

5. Anti-H. pylori medications: Amoxicillin, metronidazole, tinidazole, tetracycline

Gastrointestinal peptides

NameSourceStimulusMechanismAction
GastrinG cells (gastric antrum)Stomach distensionHormoneHCl, pepsinogen, IF secretion
Gastric motility
Trophic to gastric mucosa
CCKI cells (duodenum)Partially digested peptides and triglyceridesHormoneEnzyme rich pancreatic fluid
Gallbladder contraction and sphincter of Oddi relaxation
Gastric emptying reduction
Trophic to pancreatic acinar cells
Satiety
SecretinS cells (duodenum/proximal jejunum)Acid chyme, fatty acidsHormoneBicarbonate rich pancreatic fluid
Gastric acid reduction
Trophic to pancreatic acinar cells
VIPNeuron (GI tract, pancreas)NeuralNeurocrinePancreatic and intestinal secretion
Inhibits gastric acid and pepsinogen secretion
SomatostatinD cells (pancreas, stomach)Fat, bile salts, glucose in intestinal lumenParacrine/NeurocrineDecreases acid, pepsin, gastrin, pancreatic enzyme secretion
Decreases insulin and glucagon
Stimulates gastric mucous production


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