2: Digestion & Absorption of Carbohydrates I Carbohydrates Metabolism| Biochemistry

Introduction

This tutorial explains the digestion and absorption of carbohydrates, an essential process in biochemistry that impacts energy metabolism in the body. Understanding these mechanisms is crucial for students and professionals in fields like nutrition, medicine, and biochemistry.

Step 1: Understanding Carbohydrates

• Define carbohydrates as organic compounds made up of carbon, hydrogen, and oxygen.
• Classify carbohydrates into three main types:
  • Monosaccharides: Simple sugars like glucose and fructose.
  • Disaccharides: Composed of two monosaccharides, e.g., sucrose and lactose.
  • Polysaccharides: Long chains of monosaccharides, e.g., starch and glycogen.

Step 2: The Role of Saliva in Digestion

• Salivary amylase, an enzyme in saliva, begins the breakdown of starch into maltose.
• This process starts in the mouth and continues until food reaches the stomach.

Step 3: Stomach Digestion

• The acidic environment in the stomach halts the action of salivary amylase.
• Proteins are denatured, and gastric juices assist in the digestion of other nutrients.

Step 4: Digestion in the Small Intestine

• Upon entering the small intestine, carbohydrates are further broken down by:
  • Pancreatic amylase: Continues the breakdown of starch into disaccharides.
  • Brush border enzymes: Convert disaccharides (e.g., maltose, sucrose, lactose) into monosaccharides.

Step 5: Absorption of Monosaccharides

• Monosaccharides like glucose, fructose, and galactose are absorbed through the intestinal wall.
• Absorption occurs primarily in the jejunum of the small intestine via:
  • Active transport: Glucose and galactose are absorbed through sodium-glucose transporters (SGLT).
  • Facilitated diffusion: Fructose is absorbed via GLUT5 transporters.

Step 6: Transport to the Liver

• Once absorbed, monosaccharides enter the bloodstream and are transported to the liver via the portal vein.
• The liver regulates blood sugar levels, storing excess glucose as glycogen or releasing it into the bloodstream as needed.

Step 7: Metabolism of Carbohydrates

• In the liver, carbohydrates are metabolized through:
  • Glycogenesis: Formation of glycogen from glucose.
  • Glycogenolysis: Breakdown of glycogen into glucose when energy is needed.
  • Glycolysis: Conversion of glucose into pyruvate, which enters the Krebs cycle for energy production.

Conclusion

This tutorial covered the digestion and absorption of carbohydrates, highlighting the critical steps from ingestion to metabolism. Understanding these processes is vital for managing dietary habits and recognizing how carbohydrates influence energy levels. For further exploration, consider delving into related topics such as carbohydrate chemistry or metabolic pathways in greater detail.