Potpourri
GASTRIC PHYSIOLOGY (ACID SECRETION)
Gastric juice is a combination of parietal (acid) and non-parietal secretions
Parietal cell, located in fundus, secrete gastric acid (HCL) and intrinsic factor (IF)
Stimulant receptors: Gastrin, Histamine [via enterochromaffin-like (ECL) cells], muscarinic receptors (acetylcholine)
Gastrin (see below) = ↑ gastric acid
H2R antagonists inhibit gastric acid secretion by blocking receptors = ↓ gastric acid
Acetylcholine via Vagus nerve act on receptor and inhibit somatostatin = ↑ gastric acid
Inhibitor receptors: somatostatin (via D cells) and prostaglandins
Prostaglandin E analogs (Misoprostol) = ↓ gastric acid production; Blockers of prostaglandins (NSAIDs) = ↑ gastric acid
Proton Pump: H+ ions (acid) secreted into gastric lumen in exchange for K+; PPIs work to halt this pump
Non-parietal cells secrete water, electrolytes and mucus
The volume/acidity of gastric juice produced at any time: determined by relative proportions of parietal and non-parietal secretions
G cells, located in antrum, secrete Gastrin
Chief cells, located in body of stomach, secrete pepsinogen
Pepsinogen is converted to Pepsin in gastric lumen via gastric acid
In early years pepsin digest milk
In later life pepsin’s major substrate is meat and other proteins; Amino acids from breakdown stimulate gastrin release
Mucosal Defense Factors (Bicarbonate, Mucus, Blood flow, Prostaglandins)
Due to exposure to high concentrations of HCL, gastroduodenal epithelial cells would appear to be at risk for auto-digestion
Barrier: Surface epithelial cells secrete mucus and bicarbonate which comprises a thin alkaline protective layer
Barrier is so effective that the luminal pH can be 2 and the barrier pH can be 7
Problems occur when: Bicarb secretion suppressed; Excessive proteolysis of mucus (inflammation); Blood flow/Prostaglandin decreased
Prostaglandin protection: secretes mucus, stimulation of bicarb, maintenance of blood flow during injury; ↓ via NSAIDsRelated posts:
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