Digestive system

Science

Definition

The digestive system breaks down food into nutrients that the body can absorb and use for energy, growth, and repair. It includes the gastrointestinal tract (mouth, esophagus, stomach, small intestine, large intestine) and accessory organs (liver, pancreas, gallbladder).

How It Works

  1. Mechanical digestion begins in the mouth as teeth break food into smaller pieces and saliva adds amylase enzyme.
  2. The esophagus moves the food bolus to the stomach via peristalsis.
  3. The stomach churns food with hydrochloric acid and pepsin to form chyme.
  4. The small intestine is where most chemical digestion and nutrient absorption occur, aided by bile and pancreatic enzymes.
  5. The large intestine absorbs water and electrolytes, forming solid waste for elimination.

Examples

  • The small intestine has villi and microvilli that increase surface area for maximum nutrient absorption
  • The liver produces bile that emulsifies fats so lipase enzymes can break them down
  • The pancreas secretes bicarbonate to neutralize stomach acid entering the small intestine

Related Terms

Circulatory system Enzyme structure Macromolecules Biochemistry

Study This Concept

Practice digestive system with free review games in these units:

Biology Unit 8: Human Body Systems