Hemostasis 🩸⛓

• Calcium


  • Plays a very important role in many steps of the coagulation process along with other biological processes
  • Different from regular calcium which is great for storage and bones but not bioavailable unless in ionized form
  • We care more about ionized calcium level than regular calcium level
• Calcium


  Also referred to as factor IV in the clotting cascade
• Fibrin strands


  • Alone help to support the platelet plug and clot formation but are pretty weak on their own
  • Need to be strengthened by connecting them to each other through crosslinks
• Fibrin stabilization factor


  • Also known as activated factor XIII
  • Attaches fibrin strands to one another, forming a fiber mesh that gives the clot strength
• The goal of the clotting cascade is to enlist more and more helpers to convert more fibrinogen to fibrin as quickly as possible
• Common pathway


  Starts from the conversion of factor X to activated factor X
• Extrinsic pathway


  • Also known as the tissue factor pathway
  • Initiated by damage to tissue and vasculature, allowing blood to come into contact with tissue factor (factor III)
• Extrinsic pathway


  1. Tissue factor activates factor VII

  2. Tissue factor-activated factor VII complex converts factor X to activated factor X, starting the common pathway
• The extrinsic pathway allows for rapid activation of fibrin and helps create a more stable platelet plug in 15-30 seconds, making it the starting point for clotting cascade initiation in cases of trauma-induced bleeding
• Intrinsic pathway


  • Also known as the contact activation pathway
  • Triggered by inflammation or damage to blood/endothelial cells, often due to exposure to collagen in the subendothelial layer
• Intrinsic pathway


  1. Factor XII becomes activated

  2. Activated factor XII converts factor XI to activated factor XI

  3. Activated factor XI converts factor IX to activated factor IX

  4. Activated factor IX, along with activated factor VIII, calcium ions, and platelet phospholipids, activates factor X, joining the common pathway
• The intrinsic pathway has more steps and is the slower, secondary response, but it can produce a larger amount of fibrin to fully stabilize the clot, making it the amplification phase of the clotting cascade
• There is no factor 6 identified in the clotting cascade, and it is often referred to as unassigned
• Thrombin acts on factor 9 and the conversion of factor 5 to activated factor 5, in addition to the conversion of fibrinogen to fibrin and activation of factor 13
• Vitamin K plays an important role in the liver for the maturation of factors 2, 7, 9, and 10 in the clotting cascade
• Prothrombin time (PT) and international normalized ratio (INR)

  Coagulation study that looks at the extrinsic pathway
• Activated partial thromboplastin time (aPTT)


  Coagulation study that looks at the intrinsic pathway
• Hvorfor skal man være opmærksom på plasma konc. af frit ioniseret ca2+?


  fordi det er med at til aktivere delelementer af koagulationskaskaden (indsæt specifikt senere), hvilket kan have stor betydning for hæmostasen.
• Extrinsic pathway


  A series of reactions in coagulation that is initiated by tissue factor and measured by Prothrombin time (PT).
• Intrinsic pathway


  A series of reactions in coagulation that is initiated by a negatively charged surface and not directly measured by a specific coagulation study.
• Prothrombin time (PT)


  A coagulation study that measures the functioning of the extrinsic pathway.
• Activated partial thromboplastin time (aPTT)

  A coagulation study that indirectly measures the intrinsic pathway.