ILA Sem 2

Question 1

Why don’t we clot in everyday life?

Answer 1

There are two pathways:
Pathway 1
1. Presence of tPA, a proteins on endothelial cells that activate the conversion of plasminogen to plasmin.
2. Plasmin is able to breakdown clots by interacting with fibrin in a way that reduces platelet aggregation
3. Marcophages and phagocytic WBCs then phagocyte the debris
Pathway 2:
Nitrci oxide & prostacyclin:
They both inhibit platelet aggregation & also can act as vasodilators

Question 2

So what is the difference in action of both paracetamol and aspirin?

Answer 2

Paracetamol transiently inhibits the formations of thromboxane, a postaglandin (group of lipids made at sites of tissue damage) which prevent platelet aggregation and platelets from becoming sticky.

Aspirin supresses the production of postaglandins and thromboxane due to it’s irreversible inactivatio of the cyclooxygenase enzyme which is required for postaglandin & thromboxane synthetis. This prevent platelet aggregation & platelets from being sticky for their whole life cycle.

Question 3

What are the 4 steps of heomeostasis

Answer 3

1. Vascular spasm/ vasoconstriction
2. Formation of platelet plug: via adhesion, activation & aggregation of platelets
   - exposed collagen activates the bound platelets to produce aggregation factors

• thromboxane A2 release by platelets, able to vasoconstriction the site of platelet aggregation
• ADP released from activated platelets stimulates the release of prostacyclin and nitric oxide which inhibit platelet aggregation to limit the size of the platelet plug

3. Blood coagulation
   - activated platelets granulate - causing blood to thicken
   - Prothrombin activator is released by the platelets which converts plasma protein prothrombin into thrombin
   - Thrombin is able to convert fibrinogen into fibrin which create a mesh around the site of injury that unable further loss of cell and creates framework for plratelets to hold on to
   - Platelets begin to shrink nd tighten together
4. Clot dissolution
   - TPA, an endothelial cell protein converts plasminogen into plasmin
   - Plasmin breaks down clots by breaking down fibrin network
   - Macrophages and other phagocytes clear the debris via phagocytosis