• The digestive system consists of the alimentary canal extending from mouth to anus.
• Different parts of the alimentary canal are specialised for different functions.
• Food is broken into small particles for easy digestion and absorption.

Mouth and Buccal Cavity

• Teeth crush and grind food.
• Saliva is secreted by salivary glands.
• Saliva contains the enzyme salivary amylase.
• Salivary amylase converts starch into simple sugars.
• The tongue mixes food with saliva and helps in swallowing.
• Food becomes soft and moist for smooth passage.

Oesophagus and Peristalsis

• Food passes from mouth to stomach through the oesophagus (food pipe).
• Rhythmic contraction and relaxation of muscles push food forward.
• These movements are called peristaltic movements.

Stomach

• The stomach is a muscular expandable organ.
• Gastric glands in the stomach wall secrete:
  • Hydrochloric acid (HCl)
  • Pepsin (protein-digesting enzyme)
  • Mucus
• HCl creates an acidic medium for pepsin action.
• HCl also kills harmful germs present in food.
• Mucus protects the stomach lining from acid.
• Food is released slowly into the small intestine through a sphincter muscle.

Small Intestine

• The small intestine is the longest part of the alimentary canal.
• Complete digestion of carbohydrates, proteins, and fats occurs here.
• Herbivores have longer small intestines than carnivores.

Role of Liver

• The liver secretes bile juice.
• Bile:
  • Makes acidic food alkaline.
  • Breaks large fat globules into smaller droplets (emulsification).

Role of Pancreas

• The pancreas secretes pancreatic juice.
• Pancreatic enzymes include:
  • Trypsin → digests proteins.
  • Lipase → digests fats.

Intestinal Juice

• Intestinal glands secrete intestinal juice.
• Final digestion converts:
  • Proteins → amino acids
  • Carbohydrates → glucose
  • Fats → fatty acids and glycerol

Absorption

• The inner lining of the small intestine has finger-like projections called villi.
• Villi increase surface area for absorption.
• Villi contain many blood vessels.
• Absorbed nutrients are transported to all body cells.

Large Intestine and Egestion

• Undigested food enters the large intestine.
• Water is absorbed from the remaining material.
• Waste is removed through the anus.
• The anal sphincter controls the exit of waste.