Page 362 - Concise Pathology for Exam Preparation ( PDFDrive )

12 Haematology 347

Common pathway
Xa
Ca++
Platelets
Va V XIII

Prothrombin Thrombin

XIIIa

Plasminogen Plasmin
Stabilized clot
Fibrin FDP (cross-linked fibrin)

Inhibitors of Coagulation
The natural inhibitors of coagulation include
• Antithrombin III
• a-Macroglobulin
• Heparin cofactor II
• Protein C and protein S

Fibrinolytic System
The physiological function of the fibrinolytic system is to digest deposits of fibrin
(thrombi).

Q. Write briefly on clinicopathological features of
idiopathic thrombocytopenic purpura (ITP).

Ans. ITP, also known as primary immune thrombocytopenic purpura and autoimmune
thrombocytopenic purpura, is defined as thrombocytopenia in the absence of other causes
of thrombocytopenia.

Pathogenesis

• In ITP, an abnormal autoantibody, usually IgG with specificity for one or more platelet
membrane glycoproteins (GPs), binds to circulating platelet membranes. In persons
with chronic ITP, approximately 75% of autoantibodies are directed against platelet
GPIIb/IIIa or GPIb/IX GP complexes.
• Autoantibody-coated platelets induce Fc receptor-mediated phagocytosis by macro-
phages in the spleen. Spleen is an important organ because platelet autoantibodies are
also formed in the white pulp.

Clinical Features
• It manifests as a bleeding tendency, easy bruising (purpura); extravasation of blood from
capillaries into skin and mucous membranes (petechiae and ecchymoses) or epistaxis;
bleeding from the gums, haematuria, menorrhagia, metrorrhagia and melena are also
seen.
• Cerebral haemorrhage is the most common cause of death in severe thrombocytopenia.
• ITP can be of two types, an acute self-limiting type and a chronic recurrent type.
• Adults may be affected at any age, but most cases are diagnosed in women aged 30–40 years.
Peak age in children is 2–6 years.

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