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Knowledge of the structure and functions of blood and other aspects
of the heart and vascular system are essential parts of training
in many therapies, such as Massage, Aromatherapy, Acupuncture, Shiatsu,
and others.
This page is intended as Revision Notes for Basic / First Level
Courses in these therapies, and some ITEC Diplomas.
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Blood Clotting is one of three mechanisms that reduce
the loss of blood from broken blood vessels.
These three mechanisms are:
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Vascular Spasm - The smooth muscle in blood
vessel walls contracts immediately the blood vessel
is broken. This response reduces blood loss for some
time, while the other hemostatic mechanisms become active.
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Platelet Plug Formation - When blood platelets
encounter a damaged blood vessel they form a "platelet
plug" to help to close the gap in the broken
blood vessel. (The key stages of this process are called
platelet adhesion, platelet release reaction,
and platelet aggregation)
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Blood Clotting (Coagulation) - As described
below:
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Following damage to a blood vessel, vascular spasm occurs
to reduce blood loss while other mechanisms also take
effect:
Blood platelets congregate at the site of damage and
amass to form a platelet plug. This is the beginning
of the process of the blood "breaking down"
from is usual liquid form in such a way that its constituents
play their own parts in processes to minimise blood
loss.
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Blood normally remains in its liquid state while it
is within the blood vessels but when it leaves them
the blood may thicken and form a gel (coagulation).
Blood clotting (technically "blood coagulation")
is the process by which (liquid) blood is transformed
into a solid state.
This blood clotting is a complex process involving many
clotting factors (incl. calcium ions, enzymes, platelets,
damaged tissues) activating each other.
The three stages of this process are:
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1.
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Formation of Prothrombinase
Prothrombinase can be formed in two ways,
depending of which of two "systems"
or "pathways" apply. These are
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Intrinsic System
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This is initiated by liquid blood making
contact with a foreign surface, i.e. something
that is not part of the body; or
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Extrinsic System
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This is initiated by liquid blood making
contact with damaged tissue.
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Both the intrinsic and the extrinsic systems
involve interactions between coagulation factors.
These coagulation factors have individual names
but are often referred to by a standardised set
of Roman Numerals, e.g. Factor VIII (antihaemophilic
factor), Factor IX (Christmas factor).
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2.
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Prothrombin converted into the enzyme
Thrombin
Prothrombinase (formed in stage 1.) converts prothrombin,
which is a plasma protein that is formed in the
liver, into the enzyme thrombin.
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3.
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Fibrinogen (soluble) converted to Fibrin
(insoluble)
In turn, thrombin converts fibrinogen (which is
also a plasma protein synthesized in the liver)
into fibrin.
Fibrin is insoluble and forms the threads that
bind the clot.
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Consequences of Blood Clotting Problems:
If blood clots too quickly/easily then thrombosis
may occur. This is blood clotting in an unbroken blood vessel,
which is dangerous and can lead to strokes or heart-attacks.
Conversely, if blood takes too long to clot hemorrhage
may occur. In this case much blood may be lost from the blood
vessels, which is also dangerous.
The hereditary disorder haemophilia is a condition in which
certain coagulation factors are missing from the blood, as
a result of which the blood cannot form clots (without medical
intervention).
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This is the end of this article but further information about
the structure and
functions of blood, blood
vessels, blood pressure,
the structure and functions
of the heart, systemic
circulation, and the vascular system generally are included
on other pages of this website.
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... End of Article ...
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