Haemostasis-Platelets(physiology)

Question 1

Explain the mechanism of action for platelets.

Answer 1

•Platelets are activated by contact with collagen, ADP, thrombin, thromboxane a2, serotonin, adrenaline etc by binding to receptors of WBCs.
•Activated platelets then release several coagulation factors and platelet activating factors.
•Platelets adhere to:
-each other by adhesion receptors or integrins, and,
-endothelial cells forming a haemostatic plug in conjunction with fibrin.

Question 2

Inhibitors of platelet release (5)

Answer 2

Adenosine
Nitric oxide
Nucleotidases
Clotting factors
Prostacyclin

Question 3

Name the three phases of haemostasis

Answer 3

Vascular phase
Platelet phase
Coagulation phase

Question 4

Explain what happens in the vascular phase (4)

Answer 4

-A cut triggers vascular spasm.
-This causes the smooth muscle fibers of vessel wall to contract.
-Hence reducing the blood loss.
-This process last for about 30 minutes.

Question 5

Explain the platelet phase

Answer 5

If is divided into three:
• Platelets activation- activation by ADH, serotonin, collagen etc.
•Platelets adhesion- platelets binds to each other and to endothelial cells.
•Platelets aggregation- begins 15 sec after injury, platelets stick to each other and form platelets plug that closes small breaks.

Question 6

During which phase is fibrinogen converted to fibrin?

Answer 6

Coagulation phase

Question 7

Three pathways involved in the coagulation phase

Answer 7

Intrinsic pathway
Extrinsic pathway
Common pathway

Question 8

Explain the extrinsic pathway of the coagulation phase

Answer 8

-Occurs outside bloodstream.
-Damaged endothelial cells causes a release in tissue factor (factor 3)
-The tissue factor and other compounds causes release of enzyme complex.
-Enzyme complex activates factor X.

Question 9

Explain the intrinsic pathway of coagulation phase (3)

Answer 9

-Begins with activation of proenzymes when exposed to collagen fibers at the site of injury- within bloodstream.
-Platelets releases platelet factor 3.
-Series of reactions activates factor X.

Question 10

Explain the common pathway of the coagulation phase

Answer 10

-Where extrinsic and intrinsic pathways merge.
-Begins with activation of factor X.
-Factor X activates prothrombin activator.
-Which converts prothrombin (proenzyme) to thrombin.
-Thrombin converts fibrinogen to insoluble fibrin.
-Produces a blood clot.

Question 11

What are the two disorders linked to haemostasis?

Answer 11

Atherosclerosis (acute coronary disease)
Haemophilia