Physical or mechanical changes • The food is chewed and broken down into smaller pieces by the teeth. • It is mixed with saliva in the mouth to form a ball by the tongue. • Once swallowed, food is churned in the stomach and broken down further, while fat melts.
Chemical changes • The digestive juices in the stomach contain chemicals called enzymes, which help to convert the foods into simpler substances so they can be absorbed into the bloodstream: 1. Proteins are broken down into amino acids. 2. Carbohydrates are broken into simple sugars. 3. Fats are broken down into fatty acids and glycerol.
• Each enzyme works on a specific nutrient, e.g. the enzyme in saliva only acts on starch – it has no effect on proteins or fats.
The digestive system
Salivary glands
Tongue Epiglottis Oesophagus Liver Stomach Gallbladder Large intestine Small intestine Pancreas Duodenum
Rectum Anus
The digestive system
Discovery Learning
Find the epiglottis in the diagram of the digestive system. Find out what its function is and share your findings with the class.
