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Physiology > Haemostasis + Platelets > Flashcards

Haemostasis + Platelets Flashcards

1
Q

What is haemostasis

A

Arrest of bleeding from blood vessels and sealing them

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2
Q

What is formation of cell fragment platelets from megakaryocytes regulated by

A

Thrombopoietin in liver and kidney

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3
Q

Explain the steps of thrombopoiesis

A

Haematopoietic sc turns to common myeloid progenitor

This produces a megakaryoblast

Repeated mitosis of megakaryoblast turns to a megakaryocyte

This extends arms through the bone marrow sinusoid (stimulated by thrombopoietin)

These arms break off as platelets

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4
Q

Where are platelets stored and secreted and phagocytosed when dying

A

Stored in spleen and secreted down the sympathetic NS

Phagocytosed by liver and spleen

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5
Q

What are the 7 components of platelets

A 
1- cell membrane 
2- exterior coat 
3- tubular system
4- microtubules 
5- granules 
6- delta bodies 
7- mitochondria
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6
Q

What is importance of exterior coat in platelets

A

Glycoprotiens

For adhesion, agreggation and activation in haemostasis

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7
Q

What does the tubular system produce

A

Thromboxane A2

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8
Q

What do granules alpha do

A

Form clotting mediators like Von Willebrand , VIII and fibrinogen

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9
Q

What do delta bodies contain

A

Adp, ca2+, serotonin (for clotting)

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10
Q

What are the 3 stages of haemostasis

A

1- vascular spasm(contraction)

2- formation of platelet plug

3- blood coagulation

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11
Q

What happens in the vascular spasm

A

When there is damage in the vessel VASOCONSTRICTORS LIKE SEROTONIN AND ADH construct muscle layer to stop blood flow out

The endothelial layers between cut adhere together when contracted
This sticking is aided by platelets which are exposed to collagen

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12
Q

Why is collagen important in the adhesion of endothelial cells by platelets

A

They activate them and also attract more platelets to it

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13
Q

Explain platelet plug formation

A

Platelets adhere via the help of exterior coat and collagen

Stuck in cell wall which uses VON WILLEBRAND FACTOR

They become activated when form a plug and this causes further vasoconstriction and stimulates coagulation

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14
Q

What do normal vessels release to stop aggregation of platelets

A

Prostacyclins

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15
Q

Which molecule in coagulation causes the clot form

A

Fibrin from fibrinogen

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16
Q

Explain how fibrinogen gets converted to fibrin in the last steps of coagulation

A

Fibrinogen converted to fibrin monomers first via thrombin IIa

Fibrin monomers form fibrin polymer for clot via factor XIIIa (13) and ca2 from the delta bodies

17
Q

What activates XIIIa

A

Thrombin IIa

18
Q

What are the 2 pathways which come together to stimulate thrombin IIa

A

Intrinsic

Extrinsic

19
Q

What stimulates the cascade in the intrinsic pathway

A

Exposure to collagen and damage of vessel wall

20
Q

What stimulates extrinsic pathway needed to help intrinsic

A

Exposes tissue factor IIIa which is released by endothelial cells

21
Q

How does the extrinsic help activation of factor X which then activated thrombin IIa

A

Factor IIIa (released by endothelial cells) forms a complex with VII to activation factor X

22
Q

How does Xa allow production of thrombin IIa

A

Concerts prothrombin II via ca2+

23
Q

What are the 2 positive feedbacks in the system of coagulation

A

1- from thrombin IIa to the intrinsic pathway

2- from Xa to extrinsic pathway

24
Q

How is antithrombin an anti clotting system

A

Inhibits factors like thrombin II needed to convert fibrinogen

25
Q

How is tissue factor pathway inhibitor an anti clotting system

A

Binds to the IIIa/VII in extrinsic pathway and therefore inactivates Xa

26
Q

How can thrombin be used as negative feedback

A

When it binds to its receptors it can stimulate prostaglandins, NO and adp production

This stops platelet aggregation

27
Q

How is thrombomodulin used as an anti clotting system

A

Produced by endothelial cells and binds to thrombin IIa and stops its effects

28
Q

Which 2 proteins are activated by thrombomodulin and stop Va and VIIIa in intrinsic pathway

A

C and S

29
Q

What is fibrinolysis

A

Clot breakdown

30
Q

Which platelet growth factor recruits fibroblasts and plasmin

A

Beta

31
Q

What does fibroblast recruitment by GF b help do

A

Form scar tissue at damage site

32
Q

Why is plasmin enzyme important

A

Fragments fibrin

33
Q

What molecule activated plasmin from plasminogen

A

TPA plasminogen activator

34
Q

Why does TPA only work if clot is present

A

TPA activated by binding to fibrin which is only present in clotting

35
Q

What does Von Willebrand do to platelets

A

Stuck them to the cell wall when activated by collagen to form plug

Physiology (31 decks)

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