Blood part II

• What is the diameter range of platelets?

  1 to 4 µm
• What is the volume range of platelets?

  Approximately 6 to 7.5 fL
• How do platelets appear when stained with Wright's stain?

  They have a light violet purple granular appearance and look like "specks of dust."
• From which cells are platelets produced?

  Platelets are produced directly from the megakaryocyte cytoplasm.
• What is the composition of platelets?

  About 60% protein, 30% lipid, 8% carbohydrate, various minerals, and water.
• What are the four anatomical divisions of platelets?

  • Peripheral zone
  • Sol-gel zone
  • Organelle zone
  • Membranous system
• What is the function of the peripheral zone of platelets?

  • Composed of membranes
  • Responsible for platelet adhesion and aggregation
• What is the role of the sol-gel zone in platelets?

  • Contains microfilaments (actin and myosin) for contraction
  • Microtubules (tubulin) maintain platelet disc shape
• What is the function of the membranous system in platelets?

  • Dense tubular system for platelet activation and prostaglandin synthesis
  • Control center for platelet activation
  • Surface connecting canalicular system for granule release
• What components are found in the organelle zone of platelets?

  • Mitochondria
  • Alpha granules (50 to 80 per platelet)
  • Dense granules (2 to 7 per platelet)
• What is the normal platelet count range?

  150-400 x 10^9/L or 150-450 x 10^9/L
• What conditions can lead to thrombocytosis?


  Polycythemia vera, idiopathic thrombocythemia, CML, and splenectomy.
• What conditions can lead to thrombocytopenia?


  Thrombocytopenic purpura, aplastic anemia, acute leukemia, and pernicious anemia.
• What are the categories of platelet estimates based on count?

  • 0 – 49,000/µL: Marked Decreased
  • 50,000 – 99,000/µL: Moderate Decreased
  • 100,000 – 149,000/µL: Slight Decreased
  • 150,000 – 199,000/µL: Low Normal
  • 200,000 – 400,000/µL: Normal
  • 401,000 – 599,000/µL: Slight Increased
  • 600,000 – 800,000/µL: Moderate Increased
  • Above 800,000/µL: Marked Increased
• What is hemostasis?


  • Interaction of vasoconstriction, platelet adhesion, aggregation, and coagulation enzyme action to stop bleeding.
  • Derived from Greek meaning “the stoppage of blood flow.”
  • Retains blood within the vascular system during injury.
• What are the stages of hemostasis?

  1. Vasoconstriction

  2. Platelet plug formation

  3. Formation of blood clot
• What causes vasoconstriction during hemostasis?

  Local myogenic spasm, nervous reflexes, and release of serotonin and Thromboxane A2 from platelets.
• What is the role of von Willebrand factor (VWF) in platelet adhesion?

  VWF attaches to exposed collagen and allows platelets to adhere through GP-Ib receptors.
• What happens during platelet activation?

  Phospholipase A2 converts membrane phospholipids to arachidonic acid, which is then converted to thromboxane A2.
• What is the end result of primary hemostasis?

  • Formation of a primary hemostatic plug or platelet plug.
  • Time for bleeding to cease depends on injury depth and vessel size.
  • Superficial wounds usually stop bleeding within 10 minutes.
• What is the coagulation cascade?

  • Formation of a stable fibrin clot.
  • Coagulation factors interact on platelet surface to produce fibrin.
• What are the preferred names and synonyms for coagulation factors?

  • I: Fibrinogen
  • II: Prothrombin
  • III: Tissue thromboplastin
  • IV: Ionized Ca2+
  • V: Labile Factor
  • VII: Stable factor
  • VIII: Antihemophilic factor A
  • IX: Christmas factor
  • X: Stuart factor
  • XI: Antihemophilic factor C
  • XII: Glass factor
  • XIII: Laki-lorand factor
• What distinguishes primary hemostasis from secondary hemostasis?

  • Primary hemostasis: Rapid, short-lived response involving vascular intima and platelets.
  • Secondary hemostasis: Delayed, long-term response involving platelets and coagulation system.
• What is the purpose of fibrinolysis?

  To digest fibrin clots and keep the vascular system free of deposited fibrin.
• What laboratory test measures the effectiveness of the extrinsic pathway?

  Prothrombin Test (PT)
• What is the normal value for the Prothrombin Test (PT)?

  10 – 12 seconds
• What laboratory test measures the effectiveness of the intrinsic pathway?


  Activated Partial Thromboplastin Time (APTT)
• What is the normal value for Activated Partial Thromboplastin Time (APTT)?

  20 – 45 seconds
• What does the Thrombin Clotting Time test for?

  Fibrinogen deficiency
• What is the normal value for Thrombin Clotting Time?

  15 – 20 seconds
• What does the Stypven Time test determine?

  Coagulation factor deficiency in the common pathway
• What is the normal value for Stypven Time?

  6 – 10 seconds
• What are the causes of thrombocytopenia?

  • Increased destruction
  • Decreased production
  • Autoimmune diseases (e.g., idiopathic thrombocytopenic purpura)
  • Non-immune causes (e.g., pregnancy, HIV)
• What are some congenital platelet disorders?

  • Bernard-Soulier Syndrome
  • Von Willebrand disease
  • Glanzmann thrombasthenia
  • Gray platelet syndrome
  • Hermansky-Pudlak syndrome
• What are some acquired vascular disorders that can cause bleeding?

  • Allergic purpura (Henoch-Schonlein purpura)
  • Senile purpura
  • Drug-induced vascular purpura
  • Scurvy
• What are some coagulation disorders and their defects?

  • Owren’s disease/Parahemophilia: Defect in Factor V
  • Hemophilia A: Defect in Factor VIII
  • Hemophilia B: Defect in Factor IX
• What are the signs of bleeding disorders related to platelet defects?


  • Deficiency in number
  • Defect in function
• What is the difference between acute and delayed hemolytic transfusion reactions?

  • Acute: Occurs immediately after transfusion
  • Delayed: Occurs days to weeks after transfusion
• What is hemolytic disease of the fetus and newborn (HDFN)?

  • Condition where fetal red blood cells are destroyed by maternal antibodies.
  • Can lead to anemia and jaundice in the newborn.
• What are the prevention and treatment options for HDFN?

  • Prevention: Rh immunoglobulin administration to Rh-negative mothers.
  • Treatment: Blood transfusions and phototherapy for affected newborns.