Blood #5, Platelets & Hemostasis - Physiology


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Blood #5, Platelets & Hemostasis - Physiology

  1. 1. Platelets small granulated Non-nucleated round or oval 2 – 4 µ in diameter mm³/400000 – 150000 life span average 8 days detached bits from megakaryocyte
  2. 2. fibroblasts Production of platelets is regulated by thrombopoietin secreted by Normally endothelial cells certain leucocytes of platelets are present % 75 – 60 in the circulating blood 25 – 40 % of platelets are present in the spleen
  3. 3. Structure of platelets Granules Mitochondria Golgi zone Glycogen Microtubules Dense body Membrane Dense tubular System Microfilament Dense body in granule Open canalicular system
  4. 4. Structure of platelets I- Plasma membrane plasma membrane contains*** glycoprotein receptors For • collagen • fibrinogen • vessel von-Willebrand factor Phospholipids I ُ nclude • platelet factor 3
  5. 5. *** The plasma membrane invaginates into the interior of the platelets to form the open canalicular system serves as a pathway uptake of extra cellular calcium release of intracellular substances *** There is also a coat of glycoprotein on its surface which helps its adhesion to injured endothelium; but not to normal endothelium
  6. 6. II – Platelet cytoplasm 1- Contractile proteins actin thrombosthenine myosin enable activated platelets to change their shape
  7. 7. 2- A skeleton of microtubules that keeps the disc shape of platelets Residuals of- 3 endoplasmic reticulum Synthesis of enzymes Golgi apparatus Calcium store 4- Mitochondria and enzyme system for synthesis of ATP and ADP
  8. 8. .Lyzosomes containing hydrolytic enzymes- 5 Glycogen granules for production of energy- 6 .anaerobically 7- Enzyme system that synthesize prostaglandins from phospholipids of the Platelet membrane.
  9. 9. types of granules 2- 8 A) Dense granules contain non-protein substances ATP, ADP, Ca++) )and serotonin b) Alpha granules contain the secreted proteins • clotting factors • fibrin stabilizing factor XIII • platelet derived growth factor
  10. 10. HEMOSTASIS By Prof Sameh Shamaa Prof Of medical Oncology and Internal medicine Mansoura Faculty Of Medicine
  11. 11. HEMOSTASIS Def:- stoppage of bleeding from the blood vessels Mechanisms (I) v.c of blood vessels (II) platelet plug formation (III) Blood coagulation (fibrinogen fibrin) (IV) Clot retraction (V) fibrinolysis to dissolve the clot
  12. 12. PRIMARY HEMOSTASIS includes the processes that result in the .formation of the platelet plug -:Necessary factors The blood vessels : the vessel walls esp. the .subendothelial layer The platelets: plasma glycoproteins 2fibrinogen Willebrand factor ,which also presents inside the platelets -
  13. 13. :Mechanisms .v.c of the bl. vessel-1 Platelets adhesion to subendothelial layer, ( Willebrand- 2 (factor is necessary for this stage :adhesion of platelets- 3- platelets secretion their activation and secretion of ADP,adrenaline, noradrenaline –> aggregation & activation of other .platelets .Aggregation of platelets- 4 .Formation of capillary plug- 5
  14. 14. Coagulation of Blood Def :- represent the conversion of fibrinogen (soluble protein( to fibrin (insoluble( meshwork which occludes the point or vessel rupture.
  15. 15. First Step :Activation of factor X BY One of 2 systems: I-urgent system (Extrinsic system.( II-delayed system (Intrinsic system.(
  16. 16. systems of coagulation I-urgent system. Extrinsic system. 12-20'' (seconds( In vivo only. Due to tissue damage. II-delayed system Intrinsic system. 4-8' (minutes( In vivo & in vitro due to contact with foreign surface ↓ ↓ Tissue factor activation of contact system ↓ ↓ X < ------------------------------------IX a < ---------------- IX ↓ Xa ↓ 2- prothrombin thrombin 3-fibrinogen Fibrin
  17. 17. EXTRINSIC SYSTEM FACTORS NICESSORY ARE: Factor X Tissue factor and Factor VII Tissue F. VIIa Xa Blood vessel VII X
  18. 18. INTRINSIC SYSTEM Necessary factors: XII (Hageman factor( - Contact system XI Kallikrene kininogene - F. IX - F. VIII - F. X - Ca. ++ - phospholipids of the platelet’s membrane
  19. 19. Contact System: Foreign surface |--------------------------------------------------| Kalierne XII kininogene Fragmentation XIIa XI XIa Rest of intrinsic pathway IX
  20. 20. Rest of intrinsic pathway IX Platelets Ca ++ IXa X VIIIa VIII Xa II IIa
  21. 21. Second Step: of Coagulation Thrombin Formation: (IIa) Factors needed: - prothrombin (II) - Xa - V (acceleririe) - phospholipids - Ca + + Platelets ++Ca II IIa V,Xa
  22. 22. 3 Step :Fibrin Formation rd Fibrin Formation:------------------------ IIa XIII Ia (Fibrinogen) -------------------(Soluble fibrin) Insoluble protein XIIIa