CHAPTER 4.2 BODY DEFENCE

4.2 BODY DEFENCE

Pathogens constantly
enter our body through:

• i) respiratory system
• Ii) digestive system
• Iii) excretory system
• Iv) skin

Do you know that our body
has a strategy to defend
itself against infections?

• Human have two main
strategies to defend itself
against infections:

• A) Non- specific body defense
mechanisms ( First and
second line of defense)

• B) Specific body defense
mechanisms.

BODY DEFENCE

1st Line of defence
→ Skin and mucous membrane

2nd Line of defence
→ Phagocytosis (white blood cell)

3rd Line of defence
→ Body immune system (Antibody)





1st LINE OF DEFENCE (prevents pathogens from entering the body→ Skin and mucous membrane

SKIN

• Tough layer – difficult to be penetrated by
microorganism

• Except: if there is a wound/injured
• Sweat/sebum secreted by skin contain

chemical → kill microorganism

MUCOUS MEMBRANE

• Membrane in digestive/respiratory tract
• Mucous membrane contain enzymes which can trap and kill bacteria.
• Microorganism that enter the respiratory tract will be filtered by nasal hair

in the nose and trapped by mucus lining in the nasal cavity
• Earwax, tears, vaginal secretions = antiseptic

• Pathogens that successfully
get past the first line of defence
enter the bloodstream and face
the second line defence.

2nd LINE OF DEFENCE( Fight pathogens through Phagocytosis

• Phagocytosis occurs if microorganisms enter the body
• White blood cells → engulf and digest pathogens using enzymes through

phagocytosis.

3rd LINE OF DEFENCE
Fights pathogens by producing antibodies → Body immune

system
➢Immunity is the ability of the
body to resist pathogens before
it is infected.

➢It involves the production of
antibodies when pathogens
enter the body.

Pathogens will be attacked specifically by antibodies. Antibodies cause pathogens clump
together.
A person who has readily available antibodies is said to be immune to disease.

• ANTIBODY: protein produced by white blood cell also called immunoglobulins,
Y-shaped molecules help fight against foreign substances called antigens

• ANTIGEN: are any substance that stimulates the immune system to produce
antibodies. Antigens can be bacteria, viruses, or fungi, toxin molecules that
cause infection and disease.

Refer science info in text book page 85

Importance Of Immunisation

→ stimulate the body defence against

infections by injecting vaccines ???

VACCINE

Is a dead or weak antigen
that will

stimulate the immune
system, and produce
antibodies to fight against

specific diseases.

Children are more easily affected by the disease due to
the body immune system in the newborn babies are not

fully develop.

Thus vaccination is much needed.





Vaccination Schedule in Malaysia

TEXTBOOK → Page: 85



Passive Immunity and Active Immunity

Immunity cab be classified into two types. Passive and active immunity. Both immunities can

be obtained naturally or artificially.

Last long after infection temporary

Passive Immunity : the body gains antibody from external sources

temporary

Active Immunity : the body produces its own antibodies when stimulated by antigens

Last long after infection

STRONG • The immune system becomes weak
IMMUNE when there is an imbalance in the
SYSTEM body. Some of the reasons for the
immune system to weaken are:

Strong Immune System

• Causes of immune system failure :

➢ Stress
➢ Not getting enough rest or sleep
➢ Obesity
➢ Smoking and drinking alcohol

Strong Immune System

Practices that
strengthen the
immune
system

CHECK YOUR ANSWER..

Summative
practice
4