Control of Gastric Secretion

Control of Gastric Secretion

• Classification of Gastric Secretion

  • Exocrine secretions: gastrin, HCl, pepsinogen, intrinsic factor, mucus.
  • Endocrine secretions: gastrin (hormonal control).

• Phases of Gastric Secretion

  1. Cephalic Phase (20-30% of secretion)

     • Triggered by sight, smell, taste, or thought of food.
     • Involves brain-mediated stimuli leading to increased secretion.
     • Vagal stimulation activates parietal cells to secrete HCl.

  2. Gastric Phase (50-60% of secretion)

     • Initiated by the presence of food in the stomach.
     • Distension of the stomach and presence of peptides stimulate secretion.
     • Local reflexes and vagal response enhance gastric secretions.
     • Gastrin released from G-cells further stimulates HCl secretion.

  3. Intestinal Phase (5-10% of secretion)

     • Starts when food enters the duodenum.
     • Inhibitory phase to prevent excessive gastric activity.
     • Hormones released (e.g., secretin, cholecystokinin) reduce gastric secretion.

• Regulatory Mechanisms

  • Hormonal control:

    • Gastrin: Stimulates acid secretion and gastric motility.
    • Somatostatin: Inhibits gastrin release.
    • Secretin: Inhibits gastric acid secretion in response to acidic chyme.
    • Cholecystokinin (CCK): Reduces gastric motility and secretion.

  • Nervous control:

    • Vagal (parasympathetic) stimulation increases secretion.
    • Sympathetic stimulation generally reduces gastric secretions.

• Factors Influencing Gastric Secretion

  • Food composition (e.g., protein-rich foods enhance secretion).
  • Psychological factors (stress and anxiety can reduce secretion).
  • Medications (e.g., proton pump inhibitors decrease acid secretion).

• Physiological Effects of Gastric Secretions

  • Hydrochloric acid (HCl): Creates an acidic environment for enzyme activation and pathogen defense.
  • Pepsinogen (inactive): Converted to pepsin in acidic conditions, aiding in protein digestion.
  • Intrinsic factor: Essential for vitamin B12 absorption in the intestine.
  • Mucus: Protects stomach lining from acidic content and mechanical damage.

• Clinical Considerations

  • Disorders related to gastric secretion:
    • Hypersecretion (e.g., Zollinger-Ellison syndrome) can cause ulcers.
    • Hyposecretion (e.g., gastritis) can lead to poor digestion and absorption issues.
    • Long-term use of antacids or proton pump inhibitors affects secretion dynamics.

• Importance of Regulation

  • Proper control ensures efficient digestion and nutrient absorption.
  • Prevents damage to gastric mucosa by maintaining appropriate acidity and buffering.

Gastric Secretion Classification

• Gastric secretions are categorized as exocrine and endocrine.
• Exocrine secretions include gastrin, hydrochloric acid (HCl), pepsinogen, intrinsic factor, and mucus.
• Endocrine secretions include gastrin, acting as a hormone.

Gastric Secretion Phases

• Cephalic Phase: Triggered by the anticipation of food, responsible for 20-30% of total gastric secretion.
  • Sight, smell, taste, and even thinking about food can initiate this phase.
  • Parasympathetic nervous system (vagal stimulation) activates parietal cells to release HCl.
• Gastric Phase: Starts when food enters the stomach and contributes 50-60% of total secretion.
  • Distention of the stomach and the presence of peptides stimulate secretion.
  • Local reflexes and vagal responses enhance gastric secretions.
  • Gastrin, released from G-cells, further stimulates HCl secretion.
• Intestinal Phase: The final phase, initiated when food enters the duodenum, accounting for 5-10% of total secretion.
  • Primarily an inhibitory phase to prevent excessive gastric activity.
  • Hormones like secretin and cholecystokinin (CCK) released in the duodenum reduce gastric secretions.

Regulatory Mechanisms

• Hormonal Control:
  • Gastrin: Stimulates acid secretion and gastric motility.
  • Somatostatin: Inhibits gastrin release.
  • Secretin: Inhibits gastric acid secretion in response to acidic chyme.
  • Cholecystokinin (CCK): Reduces gastric motility and secretion.
• Nervous Control:
  • Vagal (parasympathetic) stimulation increases secretion.
  • Sympathetic stimulation generally reduces gastric secretions.

Factors Influencing Gastric Secretion

• Food Composition: Protein-rich foods enhance secretion.
• Psychological Factors: Stress and anxiety can reduce secretion.
• Medications: Proton pump inhibitors decrease acid secretion.

Physiological Effects of Gastric Secretions

• Hydrochloric Acid (HCl): Creates an acidic environment for enzyme activation and pathogen defense.
• Pepsinogen (inactive): Converted to pepsin in acidic conditions, aiding in protein digestion.
• Intrinsic Factor: Essential for vitamin B12 absorption in the intestine.
• Mucus: Protects the stomach lining from acidic content and mechanical damage.

Clinical Considerations

• Disorders related to gastric secretion:
  • Hypersecretion (e.g., Zollinger-Ellison syndrome) can cause ulcers.
  • Hyposecretion (e.g., gastritis) can lead to poor digestion and absorption issues.
  • Long-term use of antacids or proton pump inhibitors can affect secretion dynamics.

Importance of Regulation

• Proper control ensures efficient digestion and nutrient absorption.
• Maintains appropriate acidity and buffering to prevent damage to the gastric mucosa.

This quiz explores the complex mechanisms involved in the control of gastric secretion, including both exocrine and endocrine factors. You'll learn about the different phases of secretion—cephalic, gastric, and intestinal—and their triggers and effects on digestive processes.