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PSC1002-Physiology > PSC1002/L03 Haemostasis > Flashcards

PSC1002/L03 Haemostasis Flashcards

(47 cards)

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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)

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A

Conversion of fibrinogen into fibrin
RBCs enmeshed in fibrin plug

20
Q

Describe formation of fibrin polymers. (2)

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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.

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A

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

22
Q

Describe the extrinsic pathway of thrombin stimulation.

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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)

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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)

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A

Thrombin produced by extrinsic pathway feeds back
Activates intrinsic pathway

25
What is the role of anti-thrombin? (2)
Inhibits many clotting factors (inc. thrombin) Enhanced by heparin
26
Describe the tissue factor pathway inhibitor. (3)
Binds to factor III/VIIa complex Prevents activation of its substrates factor IX and X Binds factor Xa directly
27
What is stimulated by thrombin binding to its receptor?
Production of prostaglandins (PGI), nitric oxide and ADP to inhibit further platelet aggregation
28
What is the role of thrombomodulin? (4)
Expressed by endothelial cells Binds thrombin Eliminates its coagulant effects Inactivates factors Va and VIIIa
29
What do aggregated platelets secrete and what is the function?
Platelet derived growth factor B (PDGF-B) Recruits fibroblasts from surrounding tissue
30
What dissolves clots?
Fibrinolytic enzyme - plasmin
31
What activates plasmin?
Tissue plasminogen activator (t-PA), secreted by endothelial cells
32
What does tissue plasminogen factor (t-PA) need to become activated?
Binding of fibrin (Only works on clot)
33
Which clotting factors are proteases?
All other than III, V, VIII and XIII
34
Which clotting factors are glycoproteins? (3)
III, V and VIII
35
Which clotting factor is a transglutaminase?
XIII
36
What is coagulopathy?
Deficiency or dysfunction of coagulation factors
37
What is thrombocytopaenia or thrombopathy?
Quantitative or qualitative defects of platelets respectively
38
Give 3 causes of acquired disorders of haemostasis.
Renal disease - lack of thrombopoeitin Hepatic disease - lack of fibrinogen Vitamin K deficiency - lack of II, VII, IX and X Drug-induced disorders
39
Give 3 examples of inherited disorders of haemostasis.
Structural defects to vascular system Thrombotic disorder Quantitative or qualitative platelet defects Coagulopathy
40
What is Virchow's Triad of risk factors for thrombosis?
Blood stasis Changes in vessel wall Thrombogenic changes in blood
41
What effect does a thromboembolism have on blood flow and blood pressure?
Decreases volume flow from around 60% blockage Increases velocity exponentially to 85% then drops
42
When would anticoagulants be prescribed? (3)
Atrial fibrillation Aortic valve replacement Recent surgery Autoimmune disease attacking fat and protein components of blood vessel walls
43
Describe thrombocytopenia. (3)
Low platelet count Presents as petechiae, easy bruising or excessive bleeding Caused by autoimmune disease or drug induced
44
What is thrombotic thrombocytopenic purpera? (2)
Caused by formation of small clots in circulation Low platelet numbers
45
Describe von Willebrand's Disease. (4)
Lack of vWF Poor platelet aggregation Excessive gum bleeding Autosomal dominant
46
Describe haemophilia A. (2)
Factor VIII deficiency X-linked recessive
47
Describe haemophilia B. (1)
Deficiency in factor IX

PSC1002-Physiology (29 decks)

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