2.5 Role of Ca and Interaction of Both Pathways

• What role do calcium ions play in blood clotting?

  They promote or accelerate blood-clotting reactions
• What happens to blood clotting in the absence of calcium ions?

  Blood clotting does not occur
• How does calcium ion concentration affect blood clotting in the living body?

  It seldom falls low enough to affect kinetics
• How can blood be prevented from clotting when removed from a person?

  By reducing calcium ion concentration below threshold
• What substances can be used to deionize calcium ions?

  Citrate ion can react with calcium
• What is one method to precipitate calcium ions?

  Using substances such as oxalate ion
• What initiates the extrinsic pathway of blood clotting?

  • Tissue factor initiates the extrinsic pathway
• What initiates the intrinsic pathway of blood clotting?

  • Contact of Factor XII and platelets with collagen initiates the intrinsic pathway
• How do the extrinsic and intrinsic pathways of blood clotting interact after blood vessel rupture?

  Clotting occurs by both pathways simultaneously
• What is a key difference between the extrinsic and intrinsic pathways?

  The extrinsic pathway can be explosive
• How quickly can clotting occur with severe tissue trauma in the extrinsic pathway?

  In as little as 15 seconds
• How long does the intrinsic pathway usually require to cause clotting?

  Usually requires 1 to 6 minutes
• What limits the speed of completion in the extrinsic pathway?

  Amount of tissue factor and clotting factors