Topic 11: Haemostasis (without coagulation cascade) and stopping blood coagulation

Question 1

What should be mentioned in this topic?

Answer 1

• Haemostasis
• Imbalance
• Vascular Reaction
• Thrombocyte reaction
• Stopping Blood Coagulation
• Anticoagulation
• Fibrinolysis
• Thrombolysis

Question 2

Haemostasis

Answer 2

Hemostasis is a complex defence reaction which prevents the loss of blood in case on internal or external vessel injury.
Hemostasis forms a balance system. Effects causing bleeding or coagulation always occur. If any one of them prevails for a longer period it has pathologic consequences.

Question 3

Imbalance

Answer 3

• Decreased local healing
• Pathologically increased clot
  forming mechanisms
• Pathologically decreased clot
  removal
• Damaged local healing

Question 4

Vascular Reaction

Answer 4

After injury to the vessel occurs, the smooth muscles cells surrounding the area contract. This is brought about by the difference in the membrane potentials of the injured cells and the surrounding cells. Reflex contraction by the CNS also occurs. These can be completed with the effects of the humoral vasoconstrictor substances released from the injured cells. This reaction is just a temporary stage. Their duty beside the mechanical defense is decreasing of the perfusion, so that thrombocytes can stick to the injured surface more easily, which is the basis of further reactions. The reaction lasts for about 6-10 minutes.

• First line of defense
• Contraction after injury
  
  • Direct depolarisation of smooth muscle cells
  • Neural: Reflex
  • Tissue vasoconstrictor factors
  • Vasoconstrictors form platelets: Serotonin, TX2
• Significant drop in perfusion
  
  • Optimal condition for the accumulation of platelet for several minutes

Question 5

Thrombocyte Reaction

Answer 5

• Intima injury
• Primary aggregation:
• the platelet binds to the exposed collagen
  
  • The von Willebrand factor increases primary aggregation, binds the trombocytes with
    the injured surface
• Secondary activation starts
  
  • The thrombocytes bind together secrete: coagulation factors
• The production of the endothelial PGI2 and NO stops
  
  • The secretion of the thrombocytes start o The thrombin activates
  • Thrombocyte releases
• 5-HT (serotonin), ADP, PF-3, TXA, and coagulation factors
  
  • Thrombocyte stimulation, accumulation, aggregation,
• secretion: white thrombus

Question 6

Stopping Blood Coagulation

Answer 6

The inhibition of over-reaction of the coagulation mechanisms and the elimination of the formed thrombus in time are supported by an anticoagulative, fibrinolytic, and thrombolytic system activated at the beginning of the coagulation process.

Question 7

Stopping Blood Coagulation

Anticoagulation:

Answer 7

The untouched endothelial cells bind the thrombin. The thrombin activates a plasma protein, the protein-C with the help of Calcium. The active protein-C directly prevents the activation of the key enzymes of both the intrinsic and extrinsic activation complex.

Question 8

Stopping Blood Coagulation

Fibrinolysis:

Answer 8

the thrombin stimulates the activation of an inactive plasma protease, the plasminogen. The forming plasmin is one of the most effective proteolytic enzymes that dissolve the fibrin net.

Question 9

Stopping Blood Coagulation

Thrombolysis:

Answer 9

Together with the loosening of the clot the phagocytosis strating from the inside also decreases the size of the thrombus. The increasing perfusion plays a role in the demolition of the thrombus.