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Platelets
5
...
2
...
They circulate
freely in the blood and play an important role in the formation
of blood clots
...
9)
...
The same conditions will also trigger
formation of fibrin, which forms a gel
...
Box 5
...
Box 5
...
The balance between fibrin and
plasmin is an important example
of homeostasis
...
11 Prothrombin time (PT) is
a blood test that measures how
long it takes blood to coagulate
(clot) and can be used to check for
bleeding problems
...
The international normalised
ratio (INR) is another laboratory
measurement of how long it takes
blood to form a clot
...
9
...
While taking warfarin,
the patient’s blood will be
regularly tested to make sure that
the dose is correct
...
5
...
10)
...
5
...
damage to tissues and blood
vessels activates the platelets
which become sticky and
collect to form a platelet plug
and/or
a platelet plug adheres to blood
vessel walls and triggers
inflammation that results in a
cascade of enzyme activity
COAGULATION CASCADE
activated platelets release
thromboplastin (an enzyme) which, with the aid of
calcium in solution in the
plasma changes
positive feedback
amplifies response
prothrombin (an enzyme) into
thrombin (an enzyme) that converts fibrinogen to
fibrin threads which shorten, resulting in a semi-solid blood clot that
seals the site of injury, expels serum, and hardens (-> Box 5
...
10)
Box 5
...
As the body heals, bruises change
in colour as a part of the healing
process, so the age of a bruise can
be estimated by healthcare
professionals because bilirubin,
which is a greenish-yellow colour,
remains in the skin
...
Most bruises disappear without
treatment within about two
weeks, fading to a light brown
...
5
...
5
...
2 Clots in the skin
When skin is damaged, bleeding helps to carry bacteria away from the site of the
wound, and the formation of a blood clot stops blood leaking from the body and
prevents dirt from entering the wound
...
The scab falls off when the skin underneath has healed (k
3
...
5)
...
At first it looks red or pink, then
becomes a blue-black colour as it loses oxygen, although natural skin tone will affect
the colour
...
12)
...
5
...
It can happen when the lining of the blood vessel becomes roughened
or inflamed (k atherosclerosis 5
...
1) and when the blood flow becomes very
slow or stops
...
However, this normal clotting process can lead to complications when:
• the clot forms an obstruction in an artery and the tissue served by the artery
gets little or no oxygen and dies
...
• the clot forms an obstruction in a vein so that the blood cannot get back to the
heart, the tissues behind the blockage become swollen
...
13)
...
14)
...
15)
• diabetes
• obesity
• sedentary lifestyle
• raised blood cholesterol
• surgery and immobilisation
...
It causes:
• pulmonary embolism in the lungs
• heart attack in the coronary arteries
• stroke in the brain
• gangrene in the legs
...
13 Treatment for
thrombosis uses an
anticoagulant, e
...
warfarin, to
prevent any clot from getting
larger, and new clots from
forming
...
Box 5
...
Box 5
...
Risk factors for clotting also
include:
• prolonged bed rest after a fall or
surgery
• sitting for a long time on a plane
• smoking
• cancer
• pregnancy