CBSE · Class 10 · Science · Life ProcessesExplain the process of nutrition in human beings in detail. Describe the role of different parts of the alimentary canal and digestive glands in the digestion of food.

Introduction to Human Nutrition\nHuman beings are heterotrophs and exhibit holozoic nutrition, which involves five major steps: ingestion, digestion, absorption, assimilation, and egestion. The alimentary canal is a long muscular tube running from the mouth to the anus, associated with various digestive glands that secrete enzymes.

1. Mouth and Buccal Cavity (Ingestion and Initial Digestion)

• Ingestion: Food is taken into the body through the mouth.
• Teeth: Masticate the food, breaking it down into smaller particles to increase the surface area for enzyme action.
• Salivary Glands: Secretes saliva which contains the enzyme salivary amylase (ptyalin). Salivary amylase breaks down complex starch into simple sugar (maltose). Saliva also moistens the food for easy swallowing.

2. Oesophagus

• The chewed food, called bolus, passes down the food pipe or oesophagus.
• The walls of the oesophagus undergo rhythmic contractions and relaxations known as peristaltic movements to push the food forward into the stomach.

3. Stomach

• The stomach is a muscular bag-shaped organ that expands when food enters.
• Gastric Glands: Present in the stomach wall, they secrete gastric juice containing:
  • Hydrochloric Acid (HCl): Creates an acidic medium necessary for the activation of pepsin and kills harmful bacteria entering with food.
  • Pepsin: A protein-digesting enzyme that breaks down proteins into simpler peptides.
  • Mucus: Protects the inner lining of the stomach from the corrosive action of HCl.

4. Small Intestine

• It is the longest part of the alimentary canal and the site of complete digestion of carbohydrates, fats, and proteins.
• Liver: Secretes bile juice, which is stored in the gall bladder. Bile performs two functions: makes the acidic food alkaline for pancreatic enzymes to act, and emulsifies large fat globules into smaller ones.
• Pancreas: Secretes pancreatic juice containing trypsin (for protein digestion) and lipase (for emulsified fats).
• Intestinal Glands: Secretes intestinal juice (succus entericus) which finally converts proteins into amino acids, complex carbohydrates into glucose, and fats into fatty acids and glycerol.
• Absorption: The inner wall of the small intestine has finger-like projections called villi, which are richly supplied with blood vessels. Villi dramatically increase the surface area for the absorption of digested food into the bloodstream.

5. Large Intestine

• The unabsorbed food is sent to the large intestine, where more water is absorbed from this material.
• The remaining waste is expelled from the body through the anus via the rectum, a process known as egestion.