Briefly write about hormonal control of digestive secretions in humans. (IFS 2021, 8 Marks)

Introduction:

Hormonal control plays a crucial role in regulating digestive secretions in humans. Various hormones are involved in stimulating or inhibiting the release of digestive enzymes and juices in different parts of the digestive system.

Hormonal Control of Digestive Secretions in Humans

1. Gastrin

• Source: Secreted by G-cells in the stomach.
• Stimulus: Presence of food (especially proteins) in the stomach.
• Function:
  
  • Stimulates the secretion of gastric acid (HCl) by parietal cells.
  • Promotes the release of pepsinogen from chief cells.
  • Enhances gastric motility.

2. Secretin

• Source: Produced by S-cells in the duodenum.
• Stimulus: Acidic chyme entering the duodenum from the stomach.
• Function:
  
  • Stimulates the pancreas to release bicarbonate-rich pancreatic juice to neutralize acidity.
  • Inhibits gastric acid secretion.
  • Promotes bile production in the liver.

3. Cholecystokinin (CCK)

• Source: Secreted by I-cells in the duodenum and jejunum.
• Stimulus: Presence of fats and proteins in the chyme.
• Function:
  
  • Stimulates the release of pancreatic enzymes (lipase, amylase, and proteases) for digestion.
  • Causes contraction of the gallbladder to release bile.
  • Slows gastric emptying to allow efficient digestion.

4. Gastric Inhibitory Peptide (GIP)

• Source: Produced by K-cells in the duodenum and jejunum.
• Stimulus: Presence of glucose, fatty acids, and amino acids in the chyme.
• Function:
  
  • Inhibits gastric acid secretion.
  • Stimulates insulin release from the pancreas, aiding in glucose regulation.

5. Motilin

• Source: Secreted by M-cells in the small intestine.
• Stimulus: Periods of fasting (interdigestive phase).
• Function:
  
  • Initiates the migrating motor complex (MMC), which clears undigested material.
  • Enhances gastric and intestinal motility.

6. Somatostatin

• Source: Secreted by D-cells in the stomach and pancreas.
• Stimulus: High levels of HCl or low pH in the stomach.
• Function:
  
  • Inhibits secretion of gastrin, HCl, and pancreatic enzymes.
  • Reduces bile flow and motility of the digestive tract.

Conclusion:

Hormonal control of digestive secretions in humans is a complex process involving the release of various hormones at different stages of digestion. These hormones play a crucial role in ensuring the efficient breakdown and absorption of nutrients from the food we consume.