relatively thick,
impermeable layer of
epidermal cells
(overlaying a rich
vascular dermal layer).
epidermal cells
are produced at
the base of the
epidermis as
basal cells and
proliferate,
moving
outward.
become flattened and die.
dead cells contain keratin - forms a waterproof
protective layer that reduces moisture loss and
protects underlying tissues from microorganisms.
tight junctions join
epidermal cells which
impede water loss
and microbial
penetration
Secrete sebum and sweat
low pH acidic
secretions impair
bacterial growth
Lungs
bacteria
trapped by
stick mucous
in the lining of
the bronchi
and
bronchioles
Gut
bacteria destroyed by
acid secretions of the
stomach
'chemical barriers'
Cytokines
interferons
released
from cells
infected
by
viruses.
bind to uninvaded cells, causing the
production of inactive enzymes
capable of break down viral mRNA,
inhibiting protein synthesis.
when viruses enter
activated cells,
viral-blocking enzymes
are activated.
virus is unable to multiply in
newly invaded cells.
stimulate
other
immune
responses
interleukins
secreted by
macrophages
and lympocytes
regulate interactions
between various parts
of the immune system
special proteins
secreted by various
cells of the immune
system when
pathogens enter the
tissues
Inflammation
characterised by
redness, swelling or
pain
pathogens invading
tissues trigger an
inflammatory response
damaged cells release
histamine, serotonin
and other substances,
which dilate blood
vessels in the infected
area.
increased blood flow brings
monocytes and neutrophils +
plasma protein gamma
gobulins (antibodies)
capillary wall
permeability
increases leading
to tissue oedema
sometimes the
entire body is
involved
producing fever, or
pyrexia
thought to be caused by
the neutrophils and
macrophages releasing
endogenous pyrogens
(including prostaglandins)
pyrogens travel to
the hypothalamus,
turning the
thermostat up,
increasing the
body's
temperature.
directly affects bacterial metabolism
optimum temp for
bacteria is ~ 37
degrees i.e. normal
body temp
higher temperatures for
prolonged periods can
cause problems.
denaturation of body
proteins (esp. enzymes
needed for biochemical
reactions in body cells)
mild fevers cause
the spleen and
liver to remove
additional iron
from blood. most
disease causing
bacteria require
iron to reproduce
fever decreases rate
of bacterial replication
and increases body's
metabolism
(facilitating healing
and accelerating
cellular defence
mechanisms i.e.
phagocytosis)
Phagocytosis
major
function of
inflammation
is increased
phagocytosis.
main
phagocytotic
leucocytes are
monocytes
and
neutrophils
monocytes leave circulation
and transform into
macrophages in tissues. can
phagocytose ~100 bacteria
before dying
macrophages are widely
distributed in the tissues but are
particularly numerous in the gut
wall and lungs.
as part of the
inflammatory
process, they
release
interleukin-1.
smaller
neutrophils
phagocytose
~20 bacteria
before dying.
Pus is largely
formed of
dead
neutrophils
limited because if there is a
high number of pathogenic
microorganisms in the body,
the normal blood flow rate is
insufficient in bringing
enough macrophages and
neutrophils to the site of
infection.
some bacteria (tuberculosis
bacilli) can resist
phagocytosis - protective cell
walls/ proteins on the
surface.