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non-specific animal defences against pathogens (Non-specific defences-…
non-specific animal defences against pathogens
Non-specific defences- keeping pathogens out
The skin covers the body preventing entry of pathogens
The skin also produces sebum, an oily substance that inhibits the growth of pathogens
Many of the body tracts eg airway of the gas exchange system are
lined
by
mucous membranes
Mucous membranes
secrets sticky mucus that
traps microorganisms.
Also contains
lysozymes
, which break down bacterial and fungal cell walls
Also contains
phagocytes
which remove remaining pathogens
Reflexes such as
coughing
and
sneezing
help to
eject
pathogen-laden mucus
gaseous exchange system.
While
vomiting
and
diarrhoea
expel content from the gut along with infective pathogens
Blood clotting and wound repair
Cuts
breach
the skin meaning
pathogens can enter
The blood
clot rapidly
to seal the wound.
When
platelets
come into contact with
collagen
in the walls of the
damaged blood vessels,
they adhere and start to secret substances such as
Thromboplastin
An
enzyme
that triggers a
cascade
of reactions resulting in the formation of
blood clotting.
Serotonin
Makes the
smooth muscle
in the wall of the
blood vessels contract
so they
vasoconstrict
reducing supply of blood to the area.
Inflammatory response
A
localised
response to
pathogens
Results in
inflammation
at the site of the wound
Histamines
- make vessel walls more
leaky
so blood
plasma
is
forced out
The blood is then known as
tissue fluid
which
causes swelling
and
pain
.
Cytokines
-
attract
white blood cells which dispose of
pathogens
by
phagocytosis
Histamines
- make blood vessels
dilate
, causing
localised heat
and
redness
The temperature helps prevent
pathogens reproducing
non-specific defences -getting rid of pathogens
The next line of defence if pathogens get in to the body are
adaptations
That will prevent them
growing
or
destroy
them
Fevers
Normal body temperature around 37
when pathogens invade cytokines stimulates your
hypothalamus
to
reset
the
thermostat
Most pathogens reproduce at or below 37
The
immune system
works faster at higher temperatures
Phagocytosis
They are specialised white blood cells that
engulf
and
destroy
pathogens
two main types
neutrophils
and
macrophages
They build up at the site of the infection
pus
in a spot, cut or wound is made out of dead
neutrophils
and
pathogens
How it works
1)Pathogens produce a
chemical
that attracts
phagocytes
2)Phagocytes recognise
non human proteins
3)The phagocyte
engulfs
the pathogen and encloses it in a vacuole called a
phagosome
4) the
phagocyte
combines with a lysosome to form a
phagolysosome
5)
Enzymes
from the
lysosome digest
and
destroy
the
pathogen
Antibodies
y- shaped
glycoprotines
called
immunoglobulins
They bind to a
specific antigen
on the
pathogen
That has triggered the immune response
Made up of two identical long polypeptide chains called
heavy chains
And two much shorter identical chains called the
light chains
The chains are held together by
disulphide briges
They bind to
antigens
with a
protein-based
lock -and-key
The binding site is
110 amino acids
on boteh chains called the variable region
variable region
is different shape on each antibody and gives the antibody its
specificity
.
The rest of the antibody molecule is always the same, so its called the
constant region
lymphocytes and immune respocse
B lymphocytes
mature in the
Bone marrow
where as
T lymphocytes
mature in the
Thymus gland