3.5.3 Responses in the Human
[D] The Defence System
Objectives – What you will need to
know from this section
The Immune System
 Outline the Defence System including skin/mucous
membranes of breathing, reproduction and digestive
systems
 Outline the nature & role of Phagocytic white blood
cells.
 Outline the Specific Defence System, including
antigen/antibody response
 Define the term: Induced Immunity
4. An Immune System
 Immunity is the ability
of an organism to
resist infection.
 Pathogens are microorganisms [microbes]
that cause disease.
 The human body is
designed to protect
itself from foreign cells
or invaders, and we
have two lines of
defence - general and
specific.
 Our General Defence System consists of:
Skin, Mucous membranes, Platelets and White blood cells.
Our General
Defence
System
General defence system consists of:
 Barrier to entry: the skin and mucous membrane lining of
the respiratory, digestive and reproductive tract.
 The skin, acting as a structural barrier, secretes chemicals
from the sebaceous glands that harm or kill bacteria.
 The respiratory and digestive tracts as well as other organs
of the body secrete mucus and/or further chemicals that
may remove foreign particles.
Composition of Blood
Solids
Liquid
Plasma
Red Blood Cells
White Blood Cells
Platelets
LEARNING CHECK
• What is Immunity?
• What are pathogens?
• List the parts of our General defence
system.
• List the composition of blood.
• Give one function for each part named.
 Our Specific Defence System involves :
 an antigen-antibody response, involving speciliased
white blood cells, called lymphocytes and monocytes
[macrophages].
1. Lymphocytes - Stored in lymphatic system (spleen, lymph
nodes, tonsils, adenoids & thymus gland), have large
nucleus and make antibodies. (25% of white cells)
lymphocyte
2. Monocytes – digest bacteria, have kidney shaped
nucleus & live for 6-9 days (5% of white cells)
Monocytes -- [Macrophages]
 Monocytes are phagocytic white blood
cells – also called macrophages
 These engulf bacteria and viruses upon
contact.
Monocyte
Germ
“Eating”
germ
 Others secrete chemicals that stimulate general
defence and cause fever to destroy microbes at high
temperatures.
Monocyte engulfs
an invader
Monocyte engulfs a
bacterium
LEARNING CHECK
• What is meant by a “specific defence
system”?
• Name two types of White cell involved in
this system.
• What is a lymphocyte?
• What is a Monocyte?
• What does “engulf” mean?
• Can you name an animals that engulfs its
prey?
Specific defence system:
Induced Immunity
 Organs specific to the
immune system: the
spleen, thymus and
lymph nodes.
 Lymph and blood vessels
contain cells called
lymphocytes and monocytes
– both are produced in the
bone marrow and they
respond to antigens.
LYMPHATIC
SYSTEM
 Antigens are any foreign
molecules capable of
triggering an antibody
response.
Germ
(antigen)
 An antibody is a protein, made by a
lymphocyte, which sticks to an
antigen and marks it for destruction
by other defence cells [monocytes].
Antibody
monocyte
“Eating
” germ
 Antigens may be found in bacterial cell walls, viral coats,
foreign cells or produced in cancerous cells.
LYMPHATIC SYSTEM
The lymphatic system
consists of:
•
Lymphatic vessels
that that return excess
tissue fluid to the blood
circulatory system. .
•
Lymph tissue [lymph
nodes] that assist in
fighting infection in the
body.
Three functions of the
lymphatic system
1.
Drainage – returns leaked
fluid to the blood.
2.
Transport – lipids (fats) are
absorbed from the small intestine
and carried to the skin or other
organs for storage.
3.
Defence – filters blood.
Germs that invade the body will
enter the blood or tissue fluid and
eventually get filtered through the
lymph and lymph nodes, where
white cells attack and destroy them.
Swollen glands are lymph nodes
that are actively fighting germs.
LYMPHATIC
SYSTEM
 Induced immunity is immunity due to antibody
production.
 There are two types --- active and passive.
 Active immunity develops
 Passive immunity involves
after an infection or after
antibodies that we get from
vaccination (immunisation).
elsewhere, e.g. in the womb,
It provides long lasting
or from mother’s milk.
protection.
Mother’s
antibodies
Active immunity
 A vaccine is a dead microbe that is injected into the body
and triggers antibodies but does not cause the disease.
 If the real germ ever attacks you, the antibodies are
present to remove it before it can cause the disease and
do damage.
 You are then said to be immune to that disease.
Passive immunity
 Passive immunity involves antibodies that we get from
elsewhere.
 Since these are not produced by the body's own cells, it
provides only short-lived protection.
LEARNING CHECK
• Give 3 functions of the Lymphatic system.
• Distinguish between an antigen and an
antibody.
• What is Induced immunity?
• Distinguish between active and passive
induced immunity.
• What ia a vaccine?
• Explain how vaccination gives us immunity.