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PSC1002-Physiology > PSC1002/L03 Haemostasis > Flashcards

PSC1002/L03 Haemostasis Flashcards

1
Q

Define haemostasis.

A

The arrest of bleeding from a broken blood vessel from arterioles, venules and capillaries

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2
Q

Describe platelets.

A

Small cell fragments (anuclear) budded of edge of large bone marrow cells (megakaryocytes)

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3
Q

What is platelet and megakaryocyte production mediated by?

A

Thrombopoietin - hormone produced in liver and kidneys

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4
Q

Describe the process of thrombopoiesis. (3)

A

Haematopoietic stem cell differentiates into myeloid cell line
Megakaryoblast into megakaryocyte
Thrombopoietin stimulates MKC to extend arms through bone marrow sinusoids into blood vessels

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5
Q

How many platelets are produced each day?

A

10^11

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6
Q

How many platelets can a megakaryocyte produce in its lifetime?

A

1000-3000

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7
Q

Where are platelets stored and how are they released?

A

Spleen
Released by contraction of the spleen activated by SNS

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8
Q

How are platelets disposed of?

A

After 7-10 days, apoptosis and phagocytosed in liver and spleen

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9
Q

What is the role of the exterior platelet coat?

A

Rich in glycoproteins
Adhesion, aggregation and activation

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10
Q

What is the role of the platelet tubular system?

A

Site of thromboxane A2 synthesis and release

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11
Q

What is the role of alpha granules in platelets?

A

Contain clotting mediators
Including von Willebrand factor, V, VIII and fibrinogen

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12
Q

What is the role of delta (dense bodies) in platelets?

A

Contain ADP, Ca2+ and serotonin for activation and clotting

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13
Q

Name the 3 steps in haemostasis.

A

Vascular spasm
Formation of platelet plug
Blood coagulation

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14
Q

Describe vascular spasm (step 1 of haemostasis). (4)

A

Cut or tear in blood vessel
Damaged cells and platelets release vasoconstrictors
Constriction of smooth muscle layer
Minimises blood loss and pushes broken epithelium together

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15
Q

Describe platelet plug formation (step 2 of haemostasis). (2)

A

Adhesion, activation and aggregation
Platelets stick together using vWF

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16
Q

Where is von Willebrand’s factor synthesised?

A

Endothelial cells and platelets

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17
Q

Give 3 functions of the platelet plug.

A

Compaction/strengthening
Further vasoconstriction
Stimulation of the clotting cascade

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18
Q

What is the role of prostaglandin 2? Where is it synthesised?

A

Limits platelet plug to damaged region
Inhibits platelet aggregation
In normal blood vessel lining

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19
Q

Describe blood clotting (step 3 of haemostasis). (2)

A

Conversion of fibrinogen into fibrin
RBCs enmeshed in fibrin plug

20
Q

Describe formation of fibrin polymers. (2)

A

Fibrinogen into fibrin monomers stimulated by thrombin (factor IIa, protease)
Fibrin monomers into fibrin polymers stimulated by factor XIIIa

21
Q

Describe the intrinsic pathway of thrombin stimulation.

A

Initial stimulus is exposed collagen (through damage to endothelium wall)

22
Q

Describe the extrinsic pathway of thrombin stimulation.

A

Initial stimulus is blood contact with damaged tissue outside of blood vessel that exposes tissue factor (factor III, tissue thromboplastin)

23
Q

Describe the initiation phase of blood clotting. (3)

A

Tissue exposure triggers extrinsic pathway
Thrombin production
Amounts produced too small for sustained coagulation

24
Q

Describe the amplification phase of blood clotting. (2)

A

Thrombin produced by extrinsic pathway feeds back
Activates intrinsic pathway

25
Q

What is the role of anti-thrombin? (2)

A

Inhibits many clotting factors (inc. thrombin)
Enhanced by heparin

26
Q

Describe the tissue factor pathway inhibitor. (3)

A

Binds to factor III/VIIa complex
Prevents activation of its substrates factor IX and X
Binds factor Xa directly

27
Q

What is stimulated by thrombin binding to its receptor?

A

Production of prostaglandins (PGI), nitric oxide and ADP to inhibit further platelet aggregation

28
Q

What is the role of thrombomodulin? (4)

A

Expressed by endothelial cells
Binds thrombin
Eliminates its coagulant effects
Inactivates factors Va and VIIIa

29
Q

What do aggregated platelets secrete and what is the function?

A

Platelet derived growth factor B (PDGF-B)
Recruits fibroblasts from surrounding tissue

30
Q

What dissolves clots?

A

Fibrinolytic enzyme - plasmin

31
Q

What activates plasmin?

A

Tissue plasminogen activator (t-PA), secreted by endothelial cells

32
Q

What does tissue plasminogen factor (t-PA) need to become activated?

A

Binding of fibrin
(Only works on clot)

33
Q

Which clotting factors are proteases?

A

All other than III, V, VIII and XIII

34
Q

Which clotting factors are glycoproteins? (3)

A

III, V and VIII

35
Q

Which clotting factor is a transglutaminase?

A

XIII

36
Q

What is coagulopathy?

A

Deficiency or dysfunction of coagulation factors

37
Q

What is thrombocytopaenia or thrombopathy?

A

Quantitative or qualitative defects of platelets respectively

38
Q

Give 3 causes of acquired disorders of haemostasis.

A

Renal disease - lack of thrombopoeitin
Hepatic disease - lack of fibrinogen
Vitamin K deficiency - lack of II, VII, IX and X
Drug-induced disorders

39
Q

Give 3 examples of inherited disorders of haemostasis.

A

Structural defects to vascular system
Thrombotic disorder
Quantitative or qualitative platelet defects
Coagulopathy

40
Q

What is Virchow’s Triad of risk factors for thrombosis?

A

Blood stasis
Changes in vessel wall
Thrombogenic changes in blood

41
Q

What effect does a thromboembolism have on blood flow and blood pressure?

A

Decreases volume flow from around 60% blockage
Increases velocity exponentially to 85% then drops

42
Q

When would anticoagulants be prescribed? (3)

A

Atrial fibrillation
Aortic valve replacement
Recent surgery
Autoimmune disease attacking fat and protein components of blood vessel walls

43
Q

Describe thrombocytopenia. (3)

A

Low platelet count
Presents as petechiae, easy bruising or excessive bleeding
Caused by autoimmune disease or drug induced

44
Q

What is thrombotic thrombocytopenic purpera? (2)

A

Caused by formation of small clots in circulation
Low platelet numbers

45
Q

Describe von Willebrand’s Disease. (4)

A

Lack of vWF
Poor platelet aggregation
Excessive gum bleeding
Autosomal dominant

46
Q

Describe haemophilia A. (2)

A

Factor VIII deficiency
X-linked recessive

47
Q

Describe haemophilia B. (1)

A

Deficiency in factor IX

PSC1002-Physiology (29 decks)

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