The Blood Clotting Mechanism
Note: The structure and function of the heart and other aspects of the vascular system is part of training in therapies such as massage incl. Indian Head Massage, Swedish Massage, acupressure massage, aromatherapy, acupuncture, shiatsu, and others.
This page is intended to include information suitable for most basic (first level) courses in these therapies,
and some ITEC Diplomas.
Blood Clotting is one of three mechanisms that reduce
the loss of blood from broken blood vessels.
The three mechanisms are:
- 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.
- 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:
- platelet adhesion,
- platelet release reaction, and
- platelet aggregation
- Blood Clotting (Coagulation) - As described
below:
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.
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:
-
Formation of Prothrombinase
Prothrombinase can be formed in two ways,
depending of which of two "systems"
or "pathways" apply.
These are
Intrinsic System |
This is initiated by liquid blood making
contact with a foreign surface, i.e. something
that is not part of the body; or |
Extrinsic System |
This is initiated by liquid blood making
contact with damaged tissue. |
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).
- 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.
- 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.
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).
See also pages about the structure and
functions of blood, blood
vessels, blood pressure,
the structure of the heart, the functions
of the heart, and the systemic
circulation and the vascular system generally.
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