The Coagulation reference article from the English Wikipedia on 24-Jul-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Coagulation

Coagulation is the thickening or congealing of any liquid into solid clots. This article is about a specific medical usage of the term with reference to human blood's mechanisms for forming scabs over wounds.

The coagulation of human blood is a fairly complex process by which liquid blood becomes solid clots. It is an important part of hemostasis where a damaged blood vessel is ultimately covered by a fibrin clot to stop blood loss. Disorders in coagulation can lead to hemorrhage, thrombosis, or embolism.

Ordinarily coagulation is initiated within seconds after an injury occurs when platelets form a plug at the site of injury. This is called primary hemostasis. Following this, various plasma components, called clotting factors respond (in a complex cascade) to form fibrin strands which strengthen the platelet plug.

Table of contents

1 Primary hemostasis 2 The coagulation cascade 3 Disorders of Hemostasis 4 Coagulation factors 5 Laboratory tests of coagulation

Primary hemostasis

Primary hemostasis is initiated when platelets adhere, using a specific platelet collagen receptor glycoprotein Ia/IIa, to collagen fibers in vascular epithelium. This adhesion is stabilized by von Willebrand's factor which forms links between the platelet glycoprotein Ib/IX and collagen fibrils.

The platelets are then activated to secrete the contents of their granules in to the plasma, which causes a change in their shape. Fibrinogen, which links adjacent platelets by forming links via the glycoprotein IIb/IIIa.

The different pathways of the coagulation cascade.

The coagulation cascade

The coagulation cascade of secondary hemostasis is traditionally divided into three parts: the final common pathway, the intrinsic pathway (abnormal in ) and the extrinsic pathway. The pathways are a series of reactions, in which a stable form of a protein is activated to become an enzyme which then catalyzes the next reaction in the cascade. Coagulation factors are generally indicated by Roman numerals, with a lowercase a appended to indicate an active form, ultimately resulting in cross-linked fibrin.

The intrinsic pathway is initiated by activation of contact factors of plasma, and can be measured by the activated partial thromboplastin time (aPTT) test.

The extrinsic pathway is initiated by exposure of blood to "tissue factor" (a specific cellular lipoprotein), and can be measured by the prothrombin time (PT) test, sometimes reported as an INR value.

The common pathway is reached by completion of either or both of the above pathways, and results in the elaboration of thrombin.

If a coagulation factor is part of the intrinsic or extrinsic pathway, a deficiency of that factor will affect only one of the tests: thus hemophilia A, a deficiency of factor VIII, which is part of the intrinsic pathway, results in an abnormally prolonged PT test but a normal PTT test.

Disorders of Hemostasis

• disorders of the platelet and vessel wall
  • immune thrombocytopenic purpura (ITP)
  • thrombotic thrombocytopenic purpura (TTP)
  • hemolytic-uremic syndrome (HUS)
  • Glanzmann's thrombasthenia
  • Bernard-Soulier syndrome (abnormal glycoprotein Ib-IX-V complex)
  • storage pool disorders
  • paroxysmal nocturnal hemoglobinuria
  • gray platelet syndrome: deficient alpha granules.
  • delta storage pool deficiency: deficient dense granules.
• disorders of coagulation and thrombosis
  • disseminated intravascular coagulation
  • factor deficiencies
    • hemophilia A
    • hemophilia B (Christmas disease)
    • hemophilia C (Factor XI deficiency, mild bleeding tendency)
    • Von Willebrand disease (the commonest bleeding disorder)
  • factor inhibitors
• disorders predisposing to thrombosis
  • heparin-associated thrombosis, heparin-induced thrombocytopenia (or white clot syndrome)
  • antiphospholipid syndrome
    • Lupus anticoagulant
    • anticardiolipin antibody
  • factor V Leiden
  • prothrombin mutation
  • protein C deficiency
  • protein S deficiency
  • antithrombin deficiency

Coagulation factors

Coagulation factors and related substances

Number and/or name	Function
I (fibrinogen)	gels to form clot (fibrin)|
II (prothrombin)	activates I, V, VII, XIII, protein C, platelets
III
IV
V (proaccelerin)	supports X, activates II
VI
VII (stable factor)	activates IX, X
VIII (antihemophilic factor)	supports IX, activates X, crosslinks I
IX (Christmas factor)	activates X
X (Stuart-Prower factor)	activates II
XI (plasma thromboplastin antecedent)	activates XII and prekallikrein
XII (Hageman factor)	activates XI and prekallikrein
XIII (fibrin-stabilizing factor)	crosslinks fibrin and other proteins
von Willebrand factor (vWF, Factor VIII-related antigen)	binds VIII, mediates platelet adhesion
prekallikrein	activates XII and prekallikrein; cleaves high molecular weigh kininogen
high molecular weight kininogen	supports reciprocal activation of XII, CI, and prekallikrein
fibronectin	mediates cell adhesion
antithrombin III (major antithrombin)	inhibits IIa, Xa, and other proteases; cofactor for heparin
heparin cofactor II (minor antithrombin)	inhibits IIa, cofactor for heparin and dermatan sulfate
protein C	inactivates V and VIII
protein S	cofactor for activated protein C (APC, binds C4b-binding protein
plasminogen	lyses fibrin and other proteins
alpha-2-antiplasmin	inhibits plasmin
prourokinase	activates plasminogen
tissue plasminogen activator (tPA)	activates plasminogen
plasminogen activator inhibitor I	inactivates TPA
plasminogen activator inhibitor II	inactivates urokinase

Laboratory tests of coagulation

Common: APTT, INR (PT), TCT
Other: factor assays, mixing test, antiphosholipid antibodies, genetic tests, dilute Russell viper venom test (dRVVT), bleeding time

Cardiovascular system - Blood	Edit
Red blood cells - White blood cells - Platelets - Blood plasma
White blood cells
Granulocytes (Neutrophil granulocytes, Eosinophil granulocytes, Basophil granulocytes) - Lymphocytes - Monocytes
Coagulation
To be filled - FVIII- vWF

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