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.