Download Lesson 7 Immune System

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