Intro to haemostasis + role of platelets

Question 1

What are the three main components of haemostasis?

Answer 1

1) vascular constriction by smooth muscle cells
2) platelet plug
3) coagulation

Question 2

What is haemostasis?

Answer 2

Delicate balance to achieve blood flow + pressure sufficient to perfuse tissue, too much = bleeding, too little = thrombosis risk

Question 3

How do we get vasoconstriction at the site? Hint: three mechanisms

Answer 3

1) Nerve reflexes on arteries + arterioles
2) Endothelins
3) activated platelets produce serotonin + thromoxane A2, which contribute to vasoconstriction

Question 4

How many days do platelets last?

Answer 4

9 days

Question 5

What receptors do platelets have?

Answer 5

Collagen + vWF (initial activation)

ADP, serotonin + thromboxane A2 (activate more platelets)

Thrombin receptors

Question 6

What is the platelet release reaction?

Answer 6

Granules are secreted, loads of ADP, serotonin, vWF all released.

COX pathway starts - thromboxane A2 activated = vasoconstriction + more platelets activated

Question 7

How do platelets aggregate?

Answer 7

Fibrinogen or vWF bind to activated GPIIb and GPIIIa receptors, so platelets can all stick together!

Question 8

What are some causes of thrombocytopenia?

Answer 8

**Reduced production **
Shortened survival (e.g. lots of coagulation, antibodies)
Dilutional (transfusions)
Sequestration (platelets pool in big spleen)

Question 9

What could cause reduced production of platelets?

Answer 9

Chemo, radiotherapy, leukaemia, plasma cell myeloma, lymphoma,
cancer, fibrosis,

some viral infections e.g. HIV

Aplastic anaemia