Answer:
The digestive system
The human digestive system breaks food down into small molecules that can be used by cells in the body.
Explanation:
The major components of the digestive system.
The major components of the digestive system.
Image from OpenStax, CC BY 4.0
Digestion begins when food enters the mouth (oral cavity). Both mechanical and chemical digestion occur in the mouth. Teeth grind and break up food (mechanical), while an enzyme in saliva called amylase begins to break down carbohydrates (chemical).
After it is swallowed, the chewed food (now called a bolus) moves down the esophagus. The esophagus acts as a connection between the mouth and the stomach, but no digestion occurs here.
The bolus then reaches the stomach, where more mechanical and chemical digestion take place. The muscles in the stomach walls churn the bolus (mechanical), allowing it to mix with digestive enzymes and gastric acids (chemical). This process converts the bolus into a liquid called chyme.
Digestion continues in the stomach for several hours. During this time, an enzyme called pepsin breaks down most of the protein in the food.
