Lecture on Hydrochloric Acid Secretion and Related Conditions

Introduction

• Overview of the gastrointestinal tract: esophagus, stomach, and duodenum.
• Focus on hydrochloric acid (HCl) secretion in the stomach.
• Connection to peptic ulcers and heartburn.

Stomach Structure and Function

• Stomach secretes 2.5 liters of gastric juice daily.
• The stomach lumen is highly acidic with a pH of 1-2.
• Barriers:
  • Esophageal Sphincter: Prevents backflow to the esophagus.
  • Pyloric Sphincter: Prevents acid from entering the duodenum.
• HCl aids in food digestion.

Cells Involved in HCl Secretion

• Parietal Cells: Secrete HCl via a proton pump mechanism.
• ECL Cells: Secrete histamine, promoting HCl secretion.
• G Cells: Secrete gastrin, promoting HCl secretion.
• D Cells: Secrete somatostatin, inhibiting HCl secretion.
• Chief Cells: Secrete pepsinogen for protein digestion.
• Mucus Cells: Produce mucus to protect the stomach lining.

Regulation of HCl Secretion

• Stimulation of HCl Secretion:
  • Histamine from ECL binds to H2 receptors on parietal cells.
  • Gastrin from G cells binds to receptors on ECL and parietal cells.
  • Vagus Nerve: Releases acetylcholine binding to receptors on parietal and ECL cells.
• Inhibition of HCl Secretion:
  • Somatostatin from D cells inhibits secretion.
  • Prostaglandins (E2 and I2): Derived from arachidonic acid, inhibit HCl secretion and stimulate mucus production.

Conditions Related to Excess HCl Secretion

Peptic Ulcers

• Caused by imbalance between HCl and protective factors (mucus, bicarbonate).
• Risk factors include infection (e.g., Helicobacter pylori), stress, smoking, NSAIDs.
• Pathophysiology: Mucosal erosion due to digestive juices.

Heartburn and Gastric Acid Reflux

• Heartburn: Caused by acid reflux into the esophagus.
• GERD (Gastroesophageal Reflux Disease): Severe form of acid reflux.
• Contributing factors include weakening of esophageal sphincter.

Treatment Options

• Antacids: Neutralize stomach acid.
  • Example: Magnesium and aluminum salts.
• Proton Pump Inhibitors: Block acid secretion.
  • Example: Omeprazole.
• Histamine-2 Receptor Blockers: Inhibit histamine action on parietal cells.
  • Example: Cimetidine.
• Atropine: Blocks acetylcholine actions, though with complications.

Conclusion

• Overview of the physiology of HCl secretion, related diseases, and treatment options.
• Emphasis on understanding the balance between acid secretion and inhibition.