Nursing Pharmacology Chapter 27:  Gastrointestinal Drugs

• Gastric mucosa: acid secretion

  • Oxidative phosphorylation dependent secretion by parietal cells.

    • Parietal cells: found in mucosal glands of the body and fundus of the stomach.

  • Regulation of gastric acid secretion depends on many factors (chemical, neural, hormonal)

    • Stimulation

      1. Gastrin is the most potent stimulant

      2. Activation of postganglionic vagal fibers (muscarinic cholinergic parietal cells receptor activation)

      3. Role of histamine

         • Gastric mucosa contains large amounts of histamine in:

           1. Mast cell cytoplasmic granules

           2. Enterochromaffin-like cells (ECL)

         • H₂ receptor antagonists competitively inhibit histamine action on H₂ receptors, located on:

           1. Gastric parietal cells

           2. Cardiac atrial cells

           3. Uterine smooth muscle cells

         • H₂ receptor antagonists (cimetidine (Tagamet), ranitidine (Zantac), famotidine (Pepcid), nizatidine (Axid)) inhibit:

           1. Basal acid secretion

           2. Secretion in response to feeding, gastrin, histamine, hypoglycemia, or vagal stimulation

         • Histamine is the most important gastric acid secretion stimulant and is released from enterochromaffin-like cells by gastric and cholinergic activity

      4. Basolateral parietal cells membranes contain receptors for:

         • Histamine causes stimulation gastric acid secretion

         • Gastrin causes stimulation gastric acid secretion

         • Acetylcholine causes stimulation gastric acid secretion

         • Prostaglandins inhibit gastric acid secretion

         • Somatostatin inhibits gastric acid secretion

          

  • Regulation of Gastric Secretion of Hydrochloric Acid (HCl)

    "Regulation of Gastric Secretion of HCl. The solid arrows indicate stimulation; the dashed arrow indicates inhibition. " courtesy of Robert H. Parsons, Ph.D., Rensselaer Polytechnic Institute, used with permission

Friedman, L. S. and Peterson, W.L. Peptic Ulcer and Related Disorders In Harrison's Principles of Internal Medicine 14th edition, (Isselbacher, K.J., and Braunwald, E., Wilson, J.D., Martin, J.B., Fauci, A.S. and Kasper, D.L., eds) McGraw-Hill, Inc (Health Professions Division), 1998, pp. 1597-1616.