Lecture Notes: Digestive System and Stomach Function

Overview of Stomach Function

• Stomach's Role:
  • Acts like a washing machine: Mixes, churns, and grinds food.
  • Minimal absorption occurs in the stomach.
  • Converts bolus (ball of food) into chyme (liquid form).
  • Begins protein digestion due to large molecule size.

Structure of the Stomach

• Components:
  • Esophagus: tube from mouth to stomach.
  • Fundus: dome-shaped part.
  • Cardia: near the heart.
  • Muscle Layers: contract in multiple directions for effective churning.
• Internal Structure:
  • Rugae/Gastric Folds: grooved texture inside the stomach.
  • Greater and Lesser Curvatures: C-shaped curves of the stomach.

Control of Food Movement

• Sphincters:
  • Cardiac Sphincter: controls entry from esophagus to stomach.
  • Pyloric Sphincter: controls exit to small intestine.

Digestive Juices and Secretions

• Gastric Juices:
  • Composed of acid and enzymes (like Tide Pods in laundry analogy).
  • Parietal Cells: secrete hydrochloric acid.
  • Chief Cells: secrete digestive enzymes pepsinogen and gastric lipase.

Digestion Process

• Pepsinogen Activation:
  • Activated by hydrochloric acid into pepsin for protein digestion.
  • Essential to prevent self-digestion of stomach lining.
• Fat Digestion:
  • Limited initiation in the stomach due to difficulty breaking down.

Regulation of Digestive Processes

• Hormonal Control:
  • Gastrin: stimulates gastric juices.
  • Secretin and CCK: regulate secretion and movement.
• Nervous Control:
  • Parasympathetic impulses regulate while at rest.

Phases of Gastric Secretion

• Cephalic Phase:
  • Triggered by sight, sound, smell, taste of food.
  • 30-50% of digestive juices are produced.
• Gastric Phase:
  • Triggered by food presence, stomach distension.
  • Additional 40-50% of juices produced.
• Intestinal Phase:
  • Chyme enters duodenum, decreased stomach secretion needed.

Absorption in the Stomach

• Limited Absorption:
  • Alcohol, aspirin, water, glucose, salts absorbed in the stomach.
  • Major absorption occurs in the small intestine.

Factors Affecting Digestion

• Fluidity of Chyme:
  • Solids move slower than liquids.
  • Fatty foods take longest to digest.

Gastrointestinal Regulation

• Enterogastric Reflex:
  • Regulates rate of stomach emptying based on duodenum fullness.
  • CCK slows gastric emptying for efficient digestion.