Gastrointestinal

Which cells of the gastric body secrete HCl, and what stimulates them?

Parietal cells secrete HCl. They are stimulated by acetylcholine (M3, vagal), gastrin (CCK-B), and histamine (H2); histamine is the dominant potentiator. Acid is generated by the H+/K+ ATPase on the apical (luminal) membrane.

Which gastric cell secretes intrinsic factor, and what is its function?

Parietal cells secrete intrinsic factor, which binds vitamin B12 (cobalamin) to permit its absorption in the terminal ileum. Loss of parietal cells (e.g., autoimmune/chronic gastritis) causes pernicious anemia.

What do gastric chief cells secrete, and how is the product activated?

Chief cells secrete pepsinogen, the inactive zymogen. Gastric acid (low pH) cleaves pepsinogen to active pepsin, which begins protein digestion. Pepsin further activates more pepsinogen (autocatalysis).

What is the function of gastric G cells and the hormone they secrete?

G cells in the gastric antrum secrete gastrin, which stimulates acid secretion (mainly indirectly via histamine release from ECL cells) and promotes gastric mucosal growth. Gastrin is increased by stomach distension, amino acids/peptides, and vagal stimulation (via GRP); it is inhibited by low pH (somatostatin).

What is the role of somatostatin in GI physiology, and which cell secretes it?

D cells secrete somatostatin, which inhibits gastric acid, gastrin, pepsinogen, and pancreatic/biliary secretion, and decreases insulin/glucagon. It is the body's universal 'off' signal. The analog octreotide is used for acromegaly, variceal bleeding, and secretory tumors.