Platelets And Their Role In Hemostasis Flashcards
Thrombocytopenia
<1.5 L/mm3. <50,000- critical count. Hypersplenism HIV Idiopathic thrombocytopenic purpura Aplastic anemia Massive transfusion of stored blood Cytotoxic chemotherapy Irradiation of bone marrow
Thrombocytosis
Polycythemia vera Chronic myeloid leukemia Iron deficiency anemia Splenectomy Surgery Acute hemorrhage
Factors that determine platelet adhesion
Depth and degree of injury Site of injury Age of individual Hematocrit Speed of blood flow Size of blood vessel
Collagen, von Willebrand factor.
Platelet aggregation
Fibrinogen, GpIIb-IIIa, thrombin.
ADP, platelet activating factor (PAF)
Platelet function tests
Platelet count: critical count
Bleeding time: thrombasthenia
Platelet aggregation test: aggregometer, aggregating agent.
Platelet adhesiveness test: anticoagulated blood through tube containing glass beads
Clot retraction time: 50% in 1 hour.
Idiopathic thrombocytopenic purpura
Antiplatelet antibodies. Childhood, and adult.
Bleeding, skin exhibiting petrchiae or ecchymoses
Mucus mb- epistaxis, bleeding gums
Diagnosis- thrombocytopenia, anemia, anti platelet antibodies, increased no. of megakaryocytes in bone marrow
Corticosteroids, splenectomy
Hemostasis and stages
Process of arrest of bleeding while maintaining blood flow in a fluid state within the vascular system.
Primary hemostasis: temporary hemostatic plug
Secondary hemostatis: definitive hemistatic plug.
Steps of hemostasis
Vasoconstriction: smooth muscle, reduced blood flow, initially stretch induced, later chemically.
Temporary hemostatic plug: adhesion, aggregation, activation and release
Blood coagulation
Thrombopoiesis
Stem cell
Megakaryoblasts: >15, baso, multilobed nucleus
Promegakaryocytes: >20, baso, azuro, horse shoe shaped
Granular: 25-50, acido, azuro, irregular
Mature: polyploid, 25-50, smaller nucleus, many granules (alpha, dense, lysosomal, myeloperoxidase) near centrosome
Platelet: pinched off bits of cytoplasm, into circulation
Regulation of thrombopoiesis
Thrombopoietin: liver, artificially synthesized- E.coli.
Interleukins: 1,3,6,11
GM-CSF
Properties of platelets
Adhesion: Von willebrand, GpIb receptor
Bernard-Soulier, Von willebrand disease
Aggregation: fibrinogen, GpIIb-IIIa, thrombin, ADP, PAF
Activation and release: when they bind to collagen, thrombin, ADP.
Change in shape, pseudopodia, contraction, platelet release
Functions of platelets
Temporary hemostasis Blood coagulation Clot retraction Thrombolysis Phagocytosis Storage and transport Vascular growth: platelet derived growth factor (PDGF)
