


•      


Chapter 6 Key terms


digestion enzyme amylase maltose


oesophagus stomach


small intestine maltase glucose villi


pancreas liver bile large intestine faeces


In this chapter, you will learn to: / outline the stages of human nutrition / identify and explain the roles of the organs of the digestive system.


THE DIGESTIVE SYSTEM


The digestive system


The human body is made up of a number of different systems working together.


The digestive system allows the body to access nutrients from food, which are needed for energy and growth. There are five stages of human nutrition: 1. Ingestion: food is taken into the mouth


2. Digestion: food is broken down


3. Absorption: digested food is passed into the blood and carried to cells


4. Assimilation: digested food is used by the body for energy and to build new cells


5. Egestion: undigested food is released as waste


During this process, food is broken down by two types of digestion:


Physical digestion: food is broken down into smaller pieces by the teeth, tongue and churning action of the muscles in the stomach.


Chemical digestion: food is broken down further by digestive enzymes and other digestive juices in the stomach.


Assimilation Egestion :Fig. 6.1 The stages of human nutrition


An enzyme is a protein that speeds up the rate of chemical reactions in cells and is not used up in the process. In the digestive system, enzymes break down the chemicals in food into simpler forms so they are small enough to be used by the body.


? TEST TUBE 1. Why does food have to be digested in order to be useful to the body? Elements of Science 51 Absorption Ingestion


Digestion


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