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Carbohydrate Digestion

Learning Objectives

  • Understand the sites and products involved in carbohydrate digestion.

Overview of Carbohydrate Digestion

  • Carbohydrate digestion involves breaking down complex carbohydrates into simple sugars for absorption.

Stage 1: Digestion in the Mouth

  • Begins in the mouth with the action of salivary amylase.
    • Salivary Amylase:
    • Breaks down polysaccharides into smaller polysaccharides (called dextrins), maltose, and some glucose.

Stage 2: Digestion in the Stomach

  • When partially digested starches reach the stomach, the acidic environment halts digestion.
  • Low pH prevents further breakdown of carbohydrates.

Stage 3: Digestion in the Small Intestine

  • The digestion continues in the small intestine where the pH is around 8.
  • Pancreatic Amylase:
    • Hydrolyzes remaining dextrins to maltose and glucose.

Enzymatic Action in the Small Intestine

  • Enzymes produced by mucosal cells (lining the small intestine) hydrolyze:
    • Maltose (enzyme: Maltase).
    • Products: 2 Glucose molecules.
    • Lactose (enzyme: Lactase).
    • Products: Galactose and Glucose.
    • Sucrose (enzyme: Sucrase).
    • Products: Fructose and Glucose.

Absorption of Monosaccharides

  • Resulting monosaccharides (glucose, fructose, galactose) are absorbed through the intestinal wall into the bloodstream.
  • In the liver, fructose and galactose are converted into glucose, which serves as the primary energy source for:
    • Muscle contractions
    • Red blood cells
    • The brain

Summary of Key Components

  • Mouth: Initial digestion by salivary amylase.
  • Stomach: Low pH stops further carbohydrate digestion.
  • Small Intestine:
    • Pancreatic amylase continues digestion.
    • Mucosal enzymes (Maltase, Lactase, Sucrase) convert disaccharides to monosaccharides for absorption.

Digestion Pathway

  • Mouth ➔ Stomach ➔ Small Intestine ➔ Liver ➔ Bloodstream

  • Enzymes involved: Salivary Amylase, Pancreatic Amylase, Maltase, Lactase, Sucrase.

  • Important takeaway: The primary outcome of carbohydrate digestion is the conversion into glucose, which is vital for energy production in the body.