Lecture Notes: The Stomach

Overview

• Focus on the stomach's structure, functions, and processes.
• Discuss stomach anatomy, digestion, and related issues like heartburn and vomiting.

Anatomy of the Stomach

• Shape: J-shaped organ with several parts.
• Parts:
  • Cardia: Uppermost region where the esophagus meets the stomach.
  • Fundus: Dome-shaped upper part; temporary storage.
  • Body: Main central region.
  • Pylorus: Lower end leading to the small intestine.
• Muscle Layers:
  • Longitudinal muscles: Run along the length.
  • Circular muscles: Encircle the stomach.
  • Oblique muscles: Additional layer aiding digestion.
• Surface Structures:
  • Rugae: Folds that allow expansion.
  • Sphincters:
    • Cardiac sphincter: Controls entry from esophagus.
    • Pyloric sphincter: Controls exit to small intestine.

Digestion Processes

• Mechanical and Chemical Digestion:
  • Food is broken down by muscle contractions and enzymes.
• Gastric Juices:
  • Initiate breakdown of proteins and fats.
• Enzymes and Secretions:
  • Pepsinogen (from Chief cells) → Pepsin (active form, requires HCl).
  • Hydrochloric acid (from Parietal cells) converts pepsinogen.
  • Mucus (from columnar cells) protects the stomach lining.
  • Gastric lipase: Breaks down fats.
  • Intrinsic factor: Essential for vitamin B12 absorption.

Regulation of Gastric Activity

• Neural Regulation:
  • Sympathetic nervous system: Inhibits digestion.
  • Parasympathetic nervous system: Stimulates digestion.
• Hormonal Regulation:
  • Somatostatins: Slow down digestion by reducing acid production.
  • Gastrin: Increases gastric secretions.
  • CCK (Cholecystokinin): Released in small intestine, reduces gastric motility.

Phases of Gastric Secretion

• Cephalic Phase: Initiated by sight, smell, taste of food.
• Gastric Phase: Actual release of gastric juices.
• Intestinal Phase: Nutrient absorption in intestines.

Gastric Absorption and Movement

• Absorption: Minimal, includes water, salts, certain drugs, alcohol.
• Chyme: Semi-fluid mass of partly digested food.
• Peristalsis: Moves chyme through the digestive tract.
• Vomiting: Expulsion of stomach contents due to toxins or motion sickness.

Common Issues: Heartburn

• Cause: Backflow of stomach contents into esophagus.
• Symptoms: Chest pain resembling heart issues.
• Prevention:
  • Eat small meals, stay upright post-eating.
  • Avoid caffeine, nicotine, alcohol.
  • Use antacids for relief.

Next Topic: Small intestine.