Human Digestive System
The human digestive system consists of the alimentary canal and associated glands that work together to convert complex food substances into simpler, absorbable forms. This process involves mechanical breakdown (chewing) and chemical breakdown (enzymatic action). The entire system extends from the mouth to the anus and is approximately 8–9 meters long in an adult human.
Anatomy and Structure
The alimentary canal is a long, muscular tube with varying diameter. It comprises the following main parts:
- Buccal Cavity (Mouth): The entry point for food where ingestion occurs.
- Oesophagus (Food Pipe): A tube connecting the mouth to the stomach.
- Stomach: A J-shaped muscular organ for storage and partial digestion.
- Small Intestine: The longest part (coiled), site of complete digestion.
- Large Intestine: Responsible for absorption of water and minerals.
Process of Digestion
1. Ingestion and Digestion in Mouth
The process begins in the mouth. Teeth crush the food (mastication) to increase the surface area for enzyme action. The salivary glands secrete saliva, which contains the biological catalyst Salivary Amylase. This enzyme breaks down starch (complex carbohydrate) into sugar.
2. Digestion in Stomach
Food reaches the stomach via peristaltic movements. The gastric glands in the stomach wall secrete gastric juice containing three key components:
- Hydrochloric Acid (HCl): Creates an acidic medium which is necessary for the action of the enzyme pepsin. It also kills bacteria found in food.
- Pepsin: A protein-digesting enzyme that acts on proteins in the acidic medium.
- Mucus: Protects the inner lining of the stomach from the action of the acid under normal conditions.
3. Digestion in Small Intestine
The small intestine is the site of the complete digestion of carbohydrates, proteins, and fats. It receives secretions from two glands:
| Gland | Secretion | Function |
|---|---|---|
| Liver | Bile Juice | Makes the acidic food alkaline and emulsifies fats (breaks large fat globules into smaller ones). |
| Pancreas | Pancreatic Juice |
Contains enzymes:
|
Absorption and Egestion
The inner walls of the small intestine have numerous finger-like projections called villi. These villi are richly supplied with blood vessels and increase the surface area for rapid absorption of digested food.
The unabsorbed food is sent into the large intestine, where more villi absorb water from this material. The rest of the material is removed from the body via the anus (Egestion). The exit of this waste material is regulated by the anal sphincter.
Chapter Assessment
Review Questions (NCERT Based)
1. What is the role of acid in our stomach?
2. What is the function of digestive enzymes?
3. Where is bile produced and stored?
Last Updated: January 2026
Reviewed under Sarkari Service Prep Academic Policy.
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