MP Board · Class 10 · Science · Life ProcessesExplain the process of nutrition in human beings. Describe the complete path of the alimentary canal and the role of various digestive glands and their secretions in the digestion of food.

Introduction to Human Nutrition\nNutrition in human beings takes place through the digestive system, which consists of the alimentary canal and associated digestive glands. The alimentary canal is a long tube extending from the mouth to the anus. The process of nutrition involves ingestion, digestion, absorption, assimilation, and egestion.

1. Mouth and Buccal Cavity

• Ingestion: Food is taken into the body through the mouth.
• Teeth: Used for chewing and grinding the food into smaller particles.
• Salivary Glands: Secretes saliva which contains the enzyme salivary amylase (ptyalin). It breaks down complex starch into simple sugar (maltose).
• Tongue: Helps in mixing food with saliva and swallowing.

2. Oesophagus (Food Pipe)

• Food is pushed down the oesophagus by rhythmic contractions and relaxations of its walls, known as peristaltic movements.

3. Stomach

• The stomach is a muscular bag that expands when food enters.
• Gastric Glands: Secretes gastric juice containing hydrochloric acid (HCl), pepsin, and mucus.
• HCl: Creates an acidic medium which facilitates the action of the enzyme pepsin and kills harmful bacteria.
• 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 site of the complete digestion of carbohydrates, proteins, and fats. It receives secretions from two major glands:
  • Liver: Secretes bile juice, which makes the food alkaline and emulsifies large fat globules into smaller ones.
  • Pancreas: Secretes pancreatic juice containing trypsin (for proteins), lipase (for emulsified fats), and amylase (for carbohydrates).
• 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.
• Villi: Finger-like projections in the inner wall of the small intestine increase the surface area for the absorption of digested food into the blood.

5. Large Intestine

• The unabsorbed food is sent to the large intestine where water is absorbed from the material.
• The remaining waste is removed from the body through the anus via egestion regulated by the anal sphincter.