Digestive System

The human digestive system consists of the alimentary canal and accessory organs such as salivary glands, pancreas, and gall bladder. It is responsible for ingestion, digestion, and absorption of food and elimination of undigested waste materials.

Digestion is the process of breaking down large insoluble food molecules into small water-soluble food molecules which can be absorbed by the body.

The alimentary canal starts at the mouth, passes through the thorax, abdomen, and pelvis and ends at the anus. Its structure changes at different levels to enable the processes occurring at those levels. Digestive processes break down the food gradually until it is converted into a form that can be absorbed.

Enzymes play a crucial role in digestion. Enzymes are secreted by specialized glands. Some of these glands are located in the walls of the alimentary canal. Others are located outside the canal but are connected to it through ducts.

Nutrients absorbed from the digested food provide the energy and raw materials needed for survival and growth of cells.

The digestive system performs the following functions:

Ingestion: Ingestion is the process of taking food i.e. eating and drinking.

Propulsion: This mixes and moves the food down the alimentary canal.

Digestion: Digestion includes both mechanical breakdown (e.g. chewing) and enzymatic breakdown.

Absorption: Nutrients of the digested food move across the walls of absorptive surfaces of the alimentary canal into the blood and lymph capillaries.

Elimination: Food substances that cannot be absorbed are excreted from the body as faeces.

Topics in this Section

Organs of the Digestive System Structure of the Alimentary Canal
Mouth Salivary Glands
Pharynx Esophagus
Stomach Small Intestine
Large Intestine, Rectum and Anal canal Pancreas
Liver
  • Organs of the digestive system
  • Basic structure of the alimentary canal
    • Adventitia (outer covering)
    • Muscle layer
    • Submucosa
    • Mucosa
    • Nerve supply
    • Blood supply
  • Mouth
    • Tongue
    • Teeth
  • Salivary glands
    • Parotid glands
    • Submandibular glands
    • Sublingual glands
  • Pharynx
  • Esophagus
  • Stomach
    • Gastric juice and functions of the stomach
  • Small intestine
    • Chemical digestion in the small intestine
    • Absorption of nutrients
  • Large intestine (colon), rectum and anal canal
  • Pancreas
  • Liver
  • Biliary tract
    • Bile ducts
    • Gall bladder
  • Summary of digestion and absorption of nutrients
  • Metabolism
    • Metabolism of carbohydrate
    • Metabolism of protein
    • Metabolism of fat
  • Diseases of the mouth
  • Diseases of the pharynx
  • Diseases of the salivary glands
  • Diseases of the esophagus
  • Diseases of the stomach
  • Diseases of the intestines
  • Diseases of the pancreas
  • Diseases of the liver
  • Diseases of the gall bladder and bile ducts