Lecture Notes: Carbohydrate Digestion and Absorption

Lecturer: Dr. Nair

Introduction

• Focus: Carbohydrate digestion and absorption.
• Previous videos covered the digestive tract and processes in various sections.
• Current series will explore macromolecules (carbohydrates, proteins, lipids) through the digestive tract.

Overview of Digestion Process

• Digestion starts in the oral cavity (mechanical and minor chemical digestion).
• Stomach: mechanical and chemical digestion with enzymes (e.g., pepsin).
• Intestines: Further chemical digestion with pancreatic enzymes and bile.
• Absorption happens at the epithelial lining of the intestinal mucosa.
• Transition from large molecules to small molecules, favoring chemical digestion over mechanical digestion towards absorption.

Hydrolysis in Digestion

• Key Reaction: Hydrolysis (opposite of dehydration synthesis).
  • Enzymes break down large molecules into smaller ones using water.
  • Essential for breaking down proteins, carbohydrates, and lipids.
  • Importance of water in meals for hydrolysis.

Carbohydrate Digestion Process

1. Oral Cavity

   • Carbohydrates (e.g., rice, bread) enter the mouth.
   • Mechanical digestion: Chewing.
   • Chemical digestion: Salivary amylase breaks down polysaccharides into smaller polysaccharides.

2. Stomach

   • Mechanical digestion: Churning.
   • No significant chemical digestion for carbohydrates.

3. Small Intestines

   • Pancreatic amylase continues chemical digestion of polysaccharides to disaccharides.
   • Hydrolysis further breaks down bonds leading to disaccharides.
   • Disaccharides are too large for absorption through intestinal mucosa cells.
   • Enzymes at the brush border break disaccharides into monosaccharides.

Absorption of Monosaccharides

• Cotransport Mechanism:

  • Monosaccharides are absorbed with sodium via secondary active transport.
  • Sodium's concentration gradient assists monosaccharide transport into the cell.

• Diffusion Process:

  • Monosaccharides diffuse from intestinal cells to the bloodstream.
  • Facilitated diffusion through basolateral membrane proteins.
  • Simple diffusion from interstitial spaces into plasma.

• Sodium-Potassium ATPase

  • Maintains sodium gradient by exchanging sodium for potassium using ATP.
  • Ensures ongoing absorption of monosaccharides via cotransport.

Conclusion

• Process explained will be similar for proteins and lipids in future lectures.
• Understanding this pattern is crucial for learning about digestion of other macromolecules.

End of lecture recording.