PLATELET AND HEMOSTASIS

• What is produced directly from the megakaryocytes cytoplasm and are small non nucleated cells whose primary function is to prevent bleeding

  Platelets
• What is the size of platelet

  2-5 um
• This is the so called production of platelets influenced by the hormone TPO

  Thrombopoiesis
• This precursor of platelet first shows signs of granules like dense alpha granules and lysosomal granules

  Promegakaryocytes
• This precursor of platelet is the largest cells in the bone marrow

  Megakaryocytes
• About how many platelets are produced from megakaryocytes

  2000 to 4000
• The lifespan of platelets

  8 to 9 days
• About how many percentage of platelets are sequestered in the red pulp of the spleen

  20-30%
• About how many percentages of platelets are present in the blood circulation?

  70-80%
• During splenectomy since sequestred platelets are out in the circulation, what is the condition

  Thrombocytosis
• Splenomegaly is the enlargement of the spleen, due to the increase number of sequestred platelets condition occurs like

  Thrombocytopenia
• The platelets in the spleen are also called

  emergency pool
• The normal value of platelet

  150 to 400 x 10^9/L
• TPO are produced primarily in the liver, kidney, stromal cells, and smooth muscle cells
• Thrombocytopenia:

  • Decreased production
  • Increased loss or destruction
  • Increased platelet sequestration
• Decreased production

  • Aplastic anemia
  • Drug toxicity (Chlorothiazide)
  • Bone marrow tumor
• This type of aplastic anemia is due to Fanconi's anemia

  Congenital aplastic anemia
• There is decreased platelet production due to radiation, benzene, and drugs

  Acquired aplastic anemia
• Increased loss or destruction

  • Dilutional loss
  • DIC
  • ITP
• What causes increased loss or destruction of platelets which is the major effect of blood transfusion because platelets are easily removed in the circulation

  Dilutional loss
• What causes uncontrolled coagulation resulting to the consumption of platelets faster than the normal

  DIC
• What causes decreased loss platelets or destruction due to autoantibodies against platelets which immune system mistakenly attacks iits own platelet bodies

  ITP
• This type of ITP is most common in adults.

  Chronic ITP
• ITP is common in children due to viral diseases like measles and chicken pox

  Acute ITP
• Increased platelet sequestration: 50-90% sequestered when there is Splenomegaly
• This drug is used to treat fluid retention and high blood pressure that suppresses megakaryocytes

  Chlorothiazide
• This condition is the increased of platelet count over the upper normal limit

  Thrombocytosis
• Thrombocytosis

  • Primary (Autonomous)
  • Secondary (Reactive)
• This thrombocytosis is due to the uncontrolled proliferation of platelets like PV, Essential Thrombocythemia, Chronic Myelogenous Leukemia

  Primary (autonomous)
• This thrombocytosis is due to underlying disease and transient thrombocytosis like Infection, Iron Deficiency, Hemolytic anemia, Blood loss, Splenectomy

  Secondary (reactive)
• Platelet structure

  • Peripheral zone
  • Sol-gel zone
  • Organelle zone
  • Membrane system
• Platelet structure

  A) membrane system

  B) organelle zone

  C) peripheral zone

  D) structural zone

  
• Peripheral zone

  • Plasma membrane
  • Glycocalyx
• It is part of peripheral zone which is composed of proteins and lipids that forms the basic structure of platelets

  Plasma membrane
• This provides a distinct connection between the inside part of the platelet to the outside environment and absorbs albumin, fibrinogen, and other plasma proteins also made up of different glycoproteins

  Glycocalyx
• These are receptors necessary for platelet adhesion and aggregation

  glycoproteins
• receptor for Von Willebrand factor

  GP Ib-IX-V
• receptor for fibrinogen

  GP IIb-IIIa
• This platelet structure is the platelet cytoskeleton which provides structural stability for platelets and composed of 2 different proteins (actin microfilament and microtubules)

  Sol-gel zone
• This protein component of sol-gel zone serves as a contractile protein for clot retraction

  actin microfilament