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*Y2 LCRS Pharmacology* > Haemostasis and Thrombosis > Flashcards

Haemostasis and Thrombosis Flashcards

1
Q

What percentage of Total Blood volume is Red Blood Cells?

A

45%

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2
Q

What are the two functional types of Plasma Clotting Factors?

A

Procoagulants

Anticoagulants

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3
Q

Name the main Procoadulant factors:

A

Fibrinogen - I

Prothrombin - II

Factors V, VII-XIII

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4
Q

Name the main Anticoagulant factors:

A

Plasminogen

TFPI - Tissue factor pathway inhibitor

Proteins C & S

Antithrombin

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5
Q

What is Haemostasis?

A

Physiological process that causes blood coagulation to prevent excessive blood loss

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6
Q

What is Thrombosis?

A

A Pathophysiological process where a blood clot forms within a blood vessel and obstructs blood flow

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7
Q

What are Red Thrombi?

A

Venous thromboses - contains lots of erythrocytes and fibrin

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8
Q

What are White Thrombi?

A

Arterial thromboses - higher platelet component

They are white becuase of macrophages entering the lesion and becoming foam cells

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9
Q

When does a clot become life-threatening?

A

If it dislodges from the vessel and embolises

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10
Q

What is Virchow’s triad?

A

Three explanations for increased probability of Thrombus formation:

Rate of Blood Flow

Consistency of Blood

Blood Vessel Wall Integrity

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11
Q

How can rate of blood flow lead to formation of a clot?

A

Slow blood flow increases likelihood of thrombosis especially in the leg because blood pressure is low here

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12
Q

How can the consistency of blood affect the likelihood of a clot forming?

A

The balance between procoagulants and anticoagulants can change (especially in genetic conditions) and increase the chance - e.g. more pros and less antis

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13
Q

How can Blood vessel wall integrity affect the likelihood of a clot forming?

A

Injury of the blood vessel wall (tunica intima) will expose prothrombotic subendothelial structures, which increase the likelihood of thrombi forming

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14
Q

What are the three stages of Coagulation?

A

Initiation

Amplification

Propagation

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15
Q

What are the three drug classes that target different stages of coagulation?

A

Initiation - Anticoagulants

Amplification - Antiplatelets

Propagation - Thrombolytics

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16
Q

What takes place in the initiation stage of coagulation?

A

Initial Stage: small scale production of thrombin

A Tissue factor bearing cell (can be different types) in the lumen of a vein shows a tissue factor which activates Factors V & X forming the prothrombinase complex

The Prothrombinase complex converts prothrombin to thrombin

17
Q

What is the bodies normal response to the initiation stage of coagulation?

What happens in Pathological conditions?

A

Antithrombin (AT-III) is present within the blood and it inactivates factors IIa and Xa

Normally: Thrombin formed by prothrombinase complex, broken down by antithrombin

Pathologically: Too much thrombin may be formed

18
Q

Name the anticoagulants that may be used to prevent too much initial thrombin from being formed:

A

Dabigatran

Rivaroxaban

Heparin

Low molecular weight Heparins - Dalteparin

Warfarin

19
Q

What is Dabigatran?

A

Factor IIa inhibitor - Directly inhibits Thrombin

(oral)

20
Q

What is Rivaroxaban?

A

Direct inhibitor of Factor Xa - prevents activation of prothrombinase complex and therefore prevents production of Thrombin from Prothrombin

(Oral)

21
Q

What is Heparin?

A

Antithrombin potentiator - Activates AT-III reducing the amount of activation of factors II and X

(IV or SC)

22
Q

What is Dalteparin?

How do its actions compare to Heparin?

A

Low Molecular Weight Heparin

Antithrombin potentiator

Longer half-life than heparin

Activates the portion of AT-III that breaks down factor Xa more than IIa as seen in Heparin, so it’s pathway is more like Rivaroxaban

23
Q

What is Warfarin?

Why do its effects take some time to manifest?

A

Orally active Anticoagulant

Vitamin K antagonist (vitamin K epoxide reductase antagonist)

Vit-K is needed for generation of factors II, VII, IX and X

It stops production of these factors, but there is a reservoir in the blood which are used up first

24
Q

Label the Drugs that target the sites on this diagram:

A
25
Q

When may anticoagulants be clinically used?

A

To treat Venous Thromboses e.g. DVT and PE

During Surgery to prevent blood clotting

In Atrial Fibrillation to prevent stroke

26
Q

What happens in the Amplification stage of Coagulation?

A

Thrombin (which was activated by the Prothrombinase complex) interacts with platelets causing platelet activation

The platelets change shape and become more sticky and they aggregate around the area of the thrombus formation

27
Q

How are platelets activated by Thrombin?

A

Thrombin binds to Protease-activated Receptor (PAR)
PAR activation causes a release of Ca2+ from an internal store
Calcium leads to exocytosis of ADP from granules, and makes them more sticky

ADP has auto/paracrine effects - it binds to P2Y12 receptors
This causes liberation of Arachidonic acid and makes the platelets more activated and sticky

COX (cyclo-oxygenase) converts Arachidonic acid to Prostaglandins and Thromboxane A2
Thromboxane A2 increase expression of GlpIIb/IIIa on the surface - more sticky

28
Q

Name three antiplatelet drugs and show where they exert their effects on this diagram:

A

Clopidogrel

Asprin

Abciximab

29
Q

What is Clopidogrel?

A

P2Y12 receptor antagonist

Prevents platelet activation/aggregation

30
Q

What is Aspirin?

(In terms of Thrombosis)

A

Irreversible COX-1 Inhibitor

Reduces the production of TXA2 from Arachidonic acid

Reduces activity of platelets

31
Q

What is Abciximab?

A

Monoclonal antibody that is directed against GIpIIb/IIIa

Reduces platelet aggregation

(Specialist use only, and not commonly used because of effectiveness of Clopidogrel and Aspirin)

32
Q

When are Antiplatelets typically used clinically?

A

Arterial Thrombosis

Acute coronary syndromes (e.g. MI)

Atrial Fibrillation - Stroke prophylaxis

33
Q

What happens in the Propagation stage of coagulation?

A

There are now many activated platelets which cause a large-scale thrombin production on their surface

Thrombin converts Fibrinogen to Fibrin
Fibrin forms a net that traps the platelets within it

34
Q

What is the Thrombolytic drug used to bust clots of the Propagation stage?

How does it work?

A

Alteplase (Recombinant type Plasminogen activator (rt-PA))

They convert Plasminogen to Plasmin, a protease that degrades fibrin

35
Q

What are the indications for Alteplase?

A

Indications: Arterial/Venous thromboses
Stroke - first-line
STEMI?

36
Q

Where are DVTs most likely to form, and what is done to prevent this pharmacologically?

A

Popliteal veins where there is stasis

Prevented be restoring the balance of coags and anticoags

Prophylactiaclly: anticoagulants e.g. Rivaroxaban
After event like PE: Heparin

37
Q
A

*Y2 LCRS Pharmacology* (20 decks)

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