platelet formation

• hemostasis: the repairing of damaged blood vessels
• 1st step: vascular spasm: constriction of blood vessels, gives body time to repair
• 2nd step: platelets stick only to exposed collagen fibers.

  • Von Willebrand factor builds a bridge between collagen fibers and platelets.
  • Platelets then form spiked processes and become sticker.
• Step 2: platelets release two chemical messengers:

  ADP: causes more platelets to come over and stick and do the same

  Serotonin and thromboxane A2: enhance vascular spasm and platelet aggregation
• Phase 1: you are trying to end up with prothrombin activator
• Intrinsic pathway: factors are found in the blood

  • slower
  • is triggered by negative surfaces
• extrinsic pathway: factors are found outside of the blood

  • triggered by being exposed to factor under endothelium
  • a lot faster because it skips so many steps
• phase 2: prothrombin activator turns prothrombin into thrombin
• phase 3: strong mesh is formed

  • thrombin turns fibrinogen into fibrin which forms little net to close blood vessel
  • factor XIII stabilizes mesh
• fibrinolysis: plasmin digests clot and breaks down fibrin
• anticoagulants: factors that inhibit clotting
• clotting-retraction: platelets contract( muscle like) pulling on fibrin strands, squeezing serum out of clot, compacting clots and drawing together the edges of blood vessels
• platelet- derived growth factor: released by platelets stimulates smooth muscle cells and fibroblasts to rebuild vessel wall
• the body will limit normal clot growth by:

  • swift removal of clotting factors
  • inhibition of activated clotting factors
  • clotting factors have to reach a certain level
  • when clots reach blood normal start to be diluted and washed away
• antithrombin III, protein C inactivates thrombin not bound to fibrin

  • heparin enhances the activity of antithrombin
• More platelets information

  purple granules take 4-5 days and live 5-10 days

  • contains serotonin, Ca 2+, enzymes, ADP and platelets- derived growth factor (PDGF)
  • normal= 150,000-400,000 platelets/ mL of blood