Bihar Board - Class 11 biology - Chapter 16: Digestion and Absorption Handwritten Notes

Digestion and absorption are vital processes in which food is broken down into simpler molecules and absorbed into the bloodstream to provide energy and nutrients to the body. This chapter define the human digestive system and the process of human digestion, and the mechanisms of nutrient absorption.

Key Points

1. Digestive System Overview

   • Comprised of the alimentary canal (mouth, esophagus, stomach, intestines) and associated glands (salivary glands, liver, pancreas).
   • Functions to break down complex food substances into absorbable forms.

2. Processes of Digestion

   • Ingestion: Intake of food through the mouth.
   • Mechanical Digestion: Physical breakdown of food (chewing, churning in the stomach).
   • Chemical Digestion: Enzymatic breakdown of macromolecules into simpler forms.

3. Digestive Enzymes and Their Functions

   • Salivary Amylase: Breaks down starch into maltose in the mouth.
   • Pepsin: Digests proteins into peptides in the stomach.
   • Pancreatic Enzymes:
     • Lipase: Breaks down fats into fatty acids and glycerol.
     • Trypsin: Digests proteins into peptides.
     • Amylase: Converts starch into maltose.
   • Brush Border Enzymes (in the small intestine): Final breakdown of carbohydrates and proteins.

4. Key Steps of Digestion

   • Mouth: Mechanical and enzymatic breakdown of food begins.
   • Stomach: Acidic environment activates enzymes like pepsin; proteins are broken down.
   • Small Intestine: Major site of digestion and absorption with the help of bile (from the liver) and pancreatic enzymes.
   • Large Intestine: Absorbs water and minerals; forms feces.

5. Absorption of Nutrients

   • Occurs primarily in the small intestine, especially the villi and microvilli structures.
   • Carbohydrates: Absorbed as monosaccharides (e.g., glucose).
   • Proteins: Absorbed as amino acids.
   • Fats: Absorbed as fatty acids and glycerol, packaged into micelles and chylomicrons.
   • Vitamins and Minerals: Absorbed directly into the bloodstream.

6. Role of Accessory Organs

   • Liver: Produces bile, which emulsifies fats.
   • Pancreas: Secretes digestive enzymes and bicarbonate to neutralize stomach acid.
   • Gallbladder: Stores and releases bile into the small intestine.

7. Disorders of the Digestive System

   • Indigestion: Discomfort due to improper digestion.
   • Diarrhea: Excessive water loss through stools due to infections or poor absorption.
   • Constipation: Difficulty in defecation due to lack of fiber or water.
   • Jaundice: Liver disorder leading to excess bile pigments in the blood.

Conclusion

Digestion and absorption are essential for maintaining energy and nutrient balance in the body. The efficient functioning of the digestive system and associated glands ensures proper breakdown and absorption of food, supporting overall health and well-being. Understanding these processes helps in diagnosing and managing digestive disorders effectively.

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