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Grade 8 Science Module 2, Lesson 7 57 Lesson 7 Immune System Learning Outcomes After completing this lesson you will be able to Vocabulary • • defence syste identify the primary and secondary defence systems of the human body and describe their roles identify medical advances that enhance the body's defence mechanisms • skin • tears • • earwax describe the symptoms, treatment, and preventative vaccine for meningitis • saliva • gastric juices • cilia hairs • secondary defence system • white blood cells • antibodies • immunity • vaccines • antibiotics Primary Defence System Every day you come in contact with numerous disease-causing germs like bacteria, protozoans, fungi, and viruses. Although your body is bombarded with these, you usually do not become sick. The reason for this is because you have a system that fights these germs. The immune system or body defence system is this system. The first barrier your body possesses is the primary defence system. It consists of things like skin, tears, earwax, saliva, gastric juices, cilia hairs, and mucous. • • The skin, with its closely fitted cells, acts as a wall to germs. The skin is like the medieval knight's suit of armor. Tears have a high salt content that can kill germs that may enter the eyes. They also wash away dust, pollen, and mould spores. Module 2, Lesson 7 58 Grade 8 Science Cilia in your nose and other respiratory passageways, along with mucous, catch foreign particles. In the windpipe or trachea the cilia beat or move into the direction of the mouth cavity where germs can be swallowed and destroyed by gastric juices in the stomach or where they can be coughed out. Sneezing is a method of clearing passages of foreign particles as well. Questions: Primary Defence System Figure A: The cilia and mucous in the nose are part of the body's first line of defence' Fill in the blanks in the sentences that follow. 1. The nose is lined with small and sticky liquid called 2. The hairs and mucous filter and trap and 3. Trapped dust and pollen "tickle" our noses. This makes us Grade 8 Science Module 2, Lesson 7 59 Figure B 6. Harmful substances that reach the windpipe are trapped by 7. They are swept outward by microscopic hairs called 8. Cilia in the windpipe are always moving towards (the lungs, or the mouth and nose) Secondary Defence System When germs, bacteria, and other disease-causing organisms break through the first barrier or line of defence, your secondary defence system goes into action. In the case of a cut, white blood cells rush to the sight of the injury and begin eating or engulfing bacteria that have entered your body. Germs entering your blood through the respiratory tract (breathing in air that has been contaminated by someone coughing or sneezing) can cause an increase in the number of white blood cells within your circulatory system as well. This is in an effort to combat the disease that has entered your body. If the germ is a specific one and there are far too many for the white blood cells to overcome on their own, special white blood Its create particles called antibodies. Antibodi Module 2, Lesson 7 60 Questions: Secondary Defence Syste Study the pictures below. Then answer the questions. Figure C 1. What kind of blood cells fight germs in the body? 'hat is happening in the diagram above? Pure D at chi tisli substances does the body Grade 8 Science