Fatty deposits can
either block an artery
directly or increase its
chance of being
blocked by a blood clot
(thrombosis)
The blood supply can
be blocked completely
and if not restored
quickly, the affected
cells are permanently
damaged
In the coronary
arteries, this
results in a heart
attack (myocardial
infarction)
In the arteries
supplying the brain
it results in a stroke
An artery can burst
where blood builds
up behind an artery
that's been
narrowed as a result
of atherosclerosis
What happens in atherosclerosis?
Endothelium
becomes damaged
and dysfunctional
Endothelial
damage results in
HBP, which puts
extra strain on the
layer of cells
It might also occur
due to some of the
toxins from
cigarette smoke in
the bloodstream
Once the inner
lining of the artery
is breached, there's
an inflammatory
response
White blood cells
leave the blood
vessel and move
into the artery wall
These cells
accumulate
chemicals from the
blood, particularly
cholesterol
A fatty deposit
builds up, called an
atheroma
Calcium salts and fibrous
tissue also build up at the
site, resulting in a hard
swelling called a plaque on
the inner wall of the artery
The build up of fibrous
tissue means that the
artery wall loses some
of its elasticity - it
hardens
Plaques leads to the lumen
narrowing - makes it more difficult
to pump blood around the body
can lead to a rise in blood pressure
Positive
feedback
HBP and more plaques
Endothelial
damage in other
areas more likely
The fast flowing blood in arteries is
under high pressure so there is a
significant chance of damage to the walls.
The low pressure in he veins means there
is less chance of damage to the walls
Blood Clotting
Vital when a blood
vessel is damaged
The blood clot seals the
break in the blood
vessel and limits blood
loss and prevents entry
of pathogens through
any open wounds
When platelets (a type of
blood cell without a
nucleus), come into contact
with the damaged vessel
wall they change from
flattened disks to spheres
with long thin projections
Their cell surfaces change,
causing them to stick to
exposed collagen in the wall and
to each other to form a
temporary platelet plug. They
also release substances that
activate more platelets
The direct contact of
blood with collagen
triggers a cascade of
chemical changes
Usually blood
doesn't clot inside
blood vessels
Platelets don't stick to the endothelium of blood vessels.
It is very smooth and has substances on its
surface that repel the platelets. However, if
there is atherosclerosis and the endothelium is
damaged, the platelets come into contact with
the damaged surface and any exposed collagen.
The clotting cascade
results in a clot
Platelets stick to damaged
wall and to each other,
forming a platelet plug
Thromboplastin
release triggers
clotting cascade
Thromboplastin is
released from
damaged tissue
and from platelets
Ca2+ and vitamin K in
plasma must also be present
Thromboplastin activates
an enzyme that catalyses
the conversion of the
protein prothrombin into
a enzyme called thrombin
Thombin catalyses the
conversion of soluble
plasma protein,
fibrinogen, into the
insoluble protein, fibrin
A mesh of fibrin forms
that traps more
platelets and red blood
cells to form a clot
Coronary Heart Disease
Narrowing of the
coronary arteries
limits the amount
of oxygen-rich
blood reaching the
heart muscle
The result may be a
chest pain (angina)
Angina is usually
experienced during exertion
when the cardiac muscle is
working harder and needs
to respire more
Because the heart muscle
lacks oxygen, it's forced to
respire anaerobically
Results in
chemical changes
that trigger pain
If a fatty plaque ruptures,
collagen is exposed which
leads to rapid clot formation
The blood supply to the
heart may be blocked
completely
The heart muscle supplied by these
arteries doesn't receive blood so it's
said to be ischaemic (without blood)
If the affected muscle
cells are starved of
oxygen for long they will
be permanently damaged
Heart attack or myocardial infarction
Stroke
Supply of blood to the
brain briefly interrupted
is a mini-stroke
Blood clot blocks
one of the arteries
leading to the brain
is a full stroke, may
be fatal