Transcript File - Science at St. Dominics

Human Defence system
4. An Immune System
 Pathogens are micro-organisms that cause disease.
 Immunity is the ability of an organism to resist infection.
Invaders
How does the body defend itself from being infected from
disease by pathogens?
Part a – GENERAL DEFENCE
SYSTEM
How does the body defend itself from disease?
the blood stream
If we consider the human body, the infection will
spread around the body if it reaches our transport system.
How do microbes enter the body?
eyes
ears
mouth
nose
skin
cuts
genitals
A number of these places where microbes can enter the
body are defended.
Mouth
Defence in our stomach
If microbes enter through the mouth (usually on food) they will
be swallowed and enter the stomach.
Within the stomach is hydrochloric acid, which will kill them.
Nose
Defence our breathing system
Cells lining our breathing system are called cilia
produce mucus in which microbes can become
stuck. The cilia then send the mucus (including the
trapped microbes) towards the mouth and nose
where they are either swallowed or coughed up.
microbes travelling down
the trachea within inhaled
air
ciliated cells
microbes become stuck within
the mucus
mucus being made by the ciliated cells
Elevator action
coughed out
swallowed
Defence by our skin
Skin
thick layer of skin
blood capillary
Microbes have to penetrate the layer of skin that covers the
entire surface of our body. Once through this, they can then
reach the blood system.
Cuts
When you cut the skin, the blood system is exposed to the air.
Microbes could then get into the blood.
To limit this problem, the body can quickly
heal wounds by firstly clotting the blood
and secondly forming a scab over the
wound to shield the blood from the air.
Once the scab has formed, the body repairs the damaged tissue
underneath and finally fresh skin tissue is formed.
If the cut is very deep, a scar will remain after the cut has healed.
exposed
blood vessel
cut
scab has
formed over
the wound
microbes
cannot gain
entry
new
tissue
being
formed
Different defence
mechanisms
General defence system These barriers try to stop all
pathogens (non-specific defences).
1. Barriers to entry:
 The skin secretes
chemicals from the
sebaceous glands that
harm or kill bacteria.
 The respiratory,
reproductive and
digestive tracts secrete
mucus that may remove
foreign particles.
Composition of Blood
Solids
Liquid
Plasma
Red Blood Cells
White Blood Cells
Platelets
General defence system consists of:
2. White blood cells
called phagocytes
ingest harmful
foreign objects and
destroy them
White
Cells
Defenders
Part B – SPECIFIC DEFENCE
SYSTEM
 Our Specific Defence System - attacks specific invaders
 This involves an antigen-antibody response, and uses
specialised white blood cells, called lymphocytes and
monocytes both made in the bone marrow.
 Antigens are foreign
molecules capable of
triggering an antibody
response.
Germ
(antigen)
Antibody
monocyte
“Eating
” germ
Monocytes
 Monocytes are phagocytic
 These engulf a microorganism upon
contact.
Monocyte
Germ
“Eating”
germ
Once engulfed part of the invader remains on the surface of the
monocyte as an antigen.
Monocyte engulfs
an invader
Monocyte engulfs a
bacterium
2. Lymphocytes
Can either attack infected cells or produce antibodies
lymphocyte
 An antibody is a protein which sticks to an antigen and
marks it for destruction by other defence cells
1. Lymphocyte notices antigen and produces
antibodies to fit the antigen shape
2. Antibody “ clamps” the antigen
antigen site
antibody
3. Cells with antigen
become immobilised (cant
divide or spread)
and are also marked for
destruction
The
Clampers
Antigen
Antibody
Matching microbes and
antibodies
Passive and Active immunity
Induced immunity
 Protection from a disease due to the presence of an
antibody.
 passive.
 active
Natural
Antibodies develop
after infection
Artificial
Antibodies develop
after vaccination
LONG TERM IMMUNITY
 A vaccine is a dead microbe that is
injected into the body and triggers
antibodies but does not cause the
disease.
Induced immunity
 Protection from a disease due to the presence of an
antibody
 passive.
 active
Natural
Artificial
Getting the antibodies
Getting the
from elsewhere
Antibodies from
naturally
elsewhere
e.g. in the womb, or
medically e.g.
from mother’s milk.
injection
Mother’s
antibodies
SHORT TERM IMMUNITY
Review and put class into context
Phagocytic
Cells
General Defence
System
Skin
Barrier
System
Respiratory
Tract
Digestive
Tract
Defence
System
in
Humans
Invading
Organism
s
Reproductive
Tract
Specific
Defence
System
Defence
Molecules
Defence
Cells
Lymphocytes – more detail
Higher level only
Higher level –
Lymphocytes
in more detail
T lymphocytes ( also called T cells)
 Mature in the Thymus
but work in the lymph
nodes
 T cells do not produce
antibodies.
Types of T lymphocytes
 helper T cells
1. recognise antigens,
2. enlarge,
3. secrete chemicals such as interferon that stimulate
production of B cells
 killer T cells
 attack infected cells containing a foreign antigen,
 secrete a chemical called perforin that perforates the
membranes of cells ;
 suppressor T cells
 stop the immune response after the pathogen has
been destroyed.
 memory T cells
 They memorise the antigen and circulate in the
body for years
B lymphocytes
 B lymphocytes mature in
the bone marrow, before
moving to the lymph
nodes,
 When a B cell encounters matching
antigen, they divide into plasma
and memory cells.
plasma cells
 produce antibody molecules,
that bind to antigens,
immobilse pathogens and
mark them for destruction
B memory cells
 memorise the antigen and
circulate in the body for years
 Memory B cells do not engage in that first battle.
 They circulate in the body for years, and can intercept antigens
quickly if they enter the body for a second time.
Monocyte
Monocyte