Digestive System - IGCSE Biology Revision Notes

Overview

The digestive system is a vital organ system responsible for the digestion and absorption of food in the body. It includes both organs that food passes through and associated organs that assist in digestion.

Main Components

Alimentary Canal

• Mouth: Ingestion of food; mechanical digestion through the action of teeth.
• Oesophagus: Connects mouth to stomach; moves food by peristalsis.
• Stomach: Mechanical digestion through muscular contractions; chemical digestion with protease enzymes and hydrochloric acid.
• Small Intestine (Duodenum and Ileum): Completes digestion; absorption of nutrients occurs here.
• Large Intestine (Colon, Rectum, Anus): Absorbs water; forms and expels feces.

Associated Organs

• Salivary Glands: Secrete saliva containing amylase to begin starch digestion.
• Pancreas: Produces amylase, protease, and lipase; releases into the duodenum.
• Liver: Produces bile to aid fat digestion; neutralizes stomach acid.
• Gall Bladder: Stores bile, releases into duodenum.

Functions

• Ingestion: Taking in of food and drink through the mouth.
• Mechanical Digestion: Physical breakdown of food into smaller pieces.
• Chemical Digestion: Breakdown of large, insoluble molecules into small, soluble molecules.
• Absorption: Movement of nutrients into the bloodstream through the walls of the intestines.
• Egestion: Expulsion of undigested food as feces.

Digestive Process

1. Ingestion: Begins in the mouth.
2. Mechanical Digestion: Teeth and stomach churning.
3. Chemical Digestion: Enzymatic breakdown in various sections of the digestive tract.
4. Absorption: Mainly in the ileum of the small intestine.
5. Egestion: Final expulsion of waste.

Importance

• The digestive system is crucial for converting food into nutrients that the body needs for energy, growth, and cell repair.
• Absorption of nutrients into the bloodstream allows them to be distributed throughout the body and assimilated into cells.

Summary

Understanding the digestive system involves knowing both the physical passage food takes and the chemical processes that occur. The coordinated effort of the alimentary canal and associated organs ensures that nutrients are efficiently extracted and waste is expelled.

These notes cover the structure and function of the digestive system, highlighting its role in nutrition and maintaining health. The digestive system's efficiency is vital for overall well-being and energy maintenance.