The Nature of Science 10.4 Structure of the human digestive system
Mouth: Food is chewed and mixed with saliva.
Oesophagus: The tube that carries food to the stomach.
Liver: Produces a substance called bile which helps break down fat.
Stomach: Food is churned and mixed with acid and digestive juice.
Large intestine: Absorbs water and leaves undigested food which is removed as faeces.
Pancreas: Produces digestive enzymes.
Small intestine: Food is digested and then absorbed through the wall of the small
intestine into the blood.
Anus: Faeces is removed from the body through the anus.
Fig. 4 The different parts of the human digestive system. Fig. 4 The human digestive system 10.5 Nutrition
Nutrition involves the following five stages: 1. Ingestion: Taking food into the mouth. 2. Digestion: The breaking down of food into simpler molecules. It begins with physical digestion in the mouth where the food is chewed into smaller pieces by the teeth, and in the stomach where food is churned. Chemical digestion occurs in the mouth, stomach and small intestine, where food is further broken down by chemicals called enzymes.
3. Absorption: Simple food molecules pass through the walls of the small intestine into the blood.
4. Assimilation: Body cells take in food molecules from the blood for energy, growth and repair.
5. Egestion: Undigested food is passed out of the body through the anus.
Digestion There are two types of digestion: physical digestion and chemical digestion.
