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Haematology Lectures > L.12 Haemostasis I > Flashcards

L.12 Haemostasis I Flashcards

1
Q

What does haemostasis refer to?

A

The control of the clotting and coagulation pathways in blood in normal and disease states

Haemostasis is crucial for maintaining blood flow and vascular integrity.

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2
Q

What are the key components involved in haemostasis?

A
  • Constriction of blood vessels
  • Adhesion and aggregation of platelets
  • Formation of a fibrin mesh by coagulation cascade
  • Dissolution of the clot (thrombolysis or fibrinolysis)

These processes work together to prevent excessive bleeding and ensure proper healing.

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3
Q

Define thrombosis.

A

A pathological state within the vascular system resulting in inappropriate activation of the normal haemostatic process

Thrombosis can lead to serious health complications due to blocked blood flow.

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4
Q

What is a thrombus?

A

A blood clot that forms and results in the blockage of blood flow to vital areas

Thrombi can form in various locations, leading to different clinical conditions.

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5
Q

What is the primary purpose of haemostasis?

A
  • Ensure maintenance of blood flow under normal physiological conditions
  • Maintain integrity of the vasculature
  • Localise damage to the site of injury
  • Repair and re-establish blood flow through repaired blood vessels

These functions are vital for preventing blood loss and promoting healing.

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6
Q

How does vessel injury affect coagulation?

A

It initiates and terminates coagulation in a tightly regulated mechanism localized to the area of injury

This localized response is essential for effective healing and preventing excessive bleeding.

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7
Q

What role do inflammatory and immune responses play in haemostasis?

A

They coordinate with the haemostatic response to facilitate healing and repair

Inflammation is a natural response that helps in the healing process following injury.

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8
Q

What happens to the clot as part of vascular remodelling?

A

The resulting clot is removed

This process is essential for restoring normal blood flow and vessel function.

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9
Q

What is the haemostatic response designed to prevent?

A

The loss of blood into the tissues and to maintain vascular integrity

A proper haemostatic response is crucial for survival after injury.

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10
Q

What can result from a congenital or acquired deficiency of haemostatic factors?

A
  • Bleeding (haemorrhage)
  • Excessive clotting or persistence of a clot (thrombosis)

These conditions highlight the importance of balance in the haemostatic system.

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11
Q

Fill in the blank: The haemostatic response is a system in dynamic balance, between activation and _______.

A

inhibition of the pathways involved

This balance is critical for effective haemostasis.

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12
Q

What is the delicate balance maintained under normal conditions in haemostasis?

A

Formation and dissolution of thrombi

This balance prevents excessive bleeding or vaso-occlusion.

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13
Q

What can occur if the balance in haemostasis is disrupted?

A

Excessive bleeding or vaso-occlusion

Excessive bleeding results from poor clot formation or excessive fibrinolysis, while vaso-occlusion is due to uncontrolled thrombin formation.

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14
Q

Define thrombus.

A

Inappropriate formation of a blood clot in an intact blood vessel

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15
Q

Define embolus.

A

A floating clot that has dislodged from the position where it was formed

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16
Q

List the components of haemostasis.

A
  • Vascular endothelium
  • Platelets
  • Coagulation pathway
  • Pro-coagulant
  • Anti-coagulant
  • Fibrinolysis
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17
Q

What is the primary haemostatic response?

A

Rapid response to seal the injured vessel

Involves blood vessel, VWF, platelets.

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18
Q

What occurs during the secondary haemostatic response?

A

Formation and stabilization of platelet plug

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19
Q

What is the tertiary haemostatic response?

A

Fibrinolysis, degradation of fibrin clot

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20
Q

What happens to the blood vessel wall in response to trauma?

A

Platelets adhere to subendothelium and form platelet plug

Vasoconstriction occurs due to localized release of vasoactive amines.

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21
Q

What role does tissue factor play in vessel injury response?

A

Activates coagulation

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22
Q

What is the function of vWF in haemostasis?

A

Acts as a glue to stick platelets to the wall

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23
Q

What is the flow rate characteristic in the center of the vessel lumen?

A

Higher flow rates in centre of vessel lumen

Flow rates can be significantly lower at the endothelium surface.

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24
Q

Where are larger RBCs and smaller platelets concentrated in a blood vessel?

A

Larger RBCs are concentrated in centre of vessel; smaller platelets circulate near vessel wall

This is due to shear forces and flow dynamics.

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25
What is the role of the endothelial layer of intima under normal conditions?
Antithrombotic ## Footnote Prostaglandin I2 contributes to this antithrombotic property.
26
What happens to endothelial cells upon vessel injury?
Become prothrombotic ## Footnote This change is crucial for the coagulation response.
27
What is endothelin-1 and its role post-injury?
Strong vasoconstrictor released to minimize blood loss ## Footnote It plays a significant role in the body's response to vascular injury.
28
What does the adventitia express that is crucial for coagulation initiation?
Tissue factor ## Footnote This is important for the initiation of the secondary response in coagulation.
29
What is the role of Heparan Sulphate in the endothelium?
Inhibits fibrin formation ## Footnote This contributes to the anti-coagulant properties of the endothelium.
30
What is the function of enzymes present in the endothelium?
Inhibit platelet function ## Footnote This helps to maintain a non-thrombotic environment under normal conditions.
31
What are thrombomodulin and tissue factor pathway inhibitor involved in?
Control of coagulation ## Footnote They are important components in the regulation of the coagulation cascade.
32
What are prostacyclin and nitric oxide known for?
Vasodilators ## Footnote They help to maintain blood vessel dilation and prevent excessive clotting.
33
What occurs in the subendothelium following vascular injury?
Exposure of basement membrane and extracellular matrix ## Footnote This exposure is critical for the initiation of the coagulation process.
34
What components promote platelet adhesion after vascular injury?
Collagen, VWF, and fibronectin ## Footnote These factors are essential for the recruitment of platelets to the site of injury.
35
What happens to the endothelium during vascular injury?
Vasoconstricts and becomes pro-thrombotic ## Footnote This response is part of the body's mechanism to prevent blood loss.
36
What initiates coagulation in response to vascular injury?
Expression of tissue factor ## Footnote Tissue factor is a key player in the coagulation cascade following injury.
37
What is the role of plasminogen activator inhibitor (PAI-1)?
Inhibits activation of fibrinolytic system ## Footnote This helps to control the breakdown of clots and maintain hemostasis.
38
What is von Willebrand Factor (vWF)?
Large adhesive glycoprotein produced in endothelial cells and in the megakaryocytes ## Footnote vWF plays a crucial role in hemostasis by facilitating platelet adhesion and aggregation.
39
What does von Willebrand Factor bind to?
* Subendothelium collagen * GPIb on surface of non-activated platelets * GPIIbIIIa on surface of activated platelets * FVIII protecting it from proteolytic degradation ## Footnote These bindings are essential for platelet function and coagulation.
40
What are the steps involved in vasoconstriction and plug formation?
* Exposed collagen binds and activates platelets * Release of platelet factors * Attraction of more platelets * Aggregate into platelet plug ## Footnote This sequence is critical for the initial response to vascular injury.
41
What are the characteristics of platelets?
* Anucleate cells * Discoid shape * Life span of 10 days * Normal platelet count = 140 - 400 x 10^9/L ## Footnote Platelets are essential for hemostasis and can become rapidly activated upon vessel damage.
42
What can cause serious bleeding related to platelets?
Defective platelet function ## Footnote Conditions affecting platelet function can lead to increased bleeding risk.
43
What can activation of platelets in diseased blood vessels lead to?
Arterial thrombosis, i.e., stroke and myocardial infarction (MI) ## Footnote This highlights the dual role of platelets in both hemostasis and pathological thrombosis.
44
What are the functions of platelets?
* Interact with VWF to seal damaged vessel * Platelet-platelet interactions (primary response) * Negative charged surface to support coagulation complex formation (secondary response) * Deliver haemostatically active molecules locally * Localise clot formation * Promote vasoconstriction * Promote vessel repair ## Footnote These functions illustrate the multifaceted role of platelets in hemostasis.
45
What is the process of platelet adhesion?
Occurs within 3 seconds, involving platelet-endothelial cell interaction causing shape change and ADP release ## Footnote This rapid response is crucial for the initial phase of clot formation.
46
What occurs during platelet aggregation?
Takes about 10 seconds, resulting in formation of platelet plug and secretion from alpha-granules and dense bodies ## Footnote This is a key step in the primary hemostatic response.
47
How long does coagulation take in the clot formation process?
Approximately 5 minutes, leading to fibrin formation (secondary response) ## Footnote This step solidifies the platelet plug into a stable clot.
48
What anchors to exposed collagen during platelet tethering?
VWF ## Footnote VWF (von Willebrand Factor) plays a crucial role in platelet adhesion by anchoring to collagen.
49
What facilitates the unravelling of VWF to expose the GP1b-binding site?
Blood flow ## Footnote Blood flow is essential for the mechanical processes that expose binding sites on VWF.
50
What do platelets bind to for tethering via VWF?
GPIb ## Footnote GPIb is a glycoprotein that is constitutively expressed on platelets and is crucial for their adhesion.
51
What occurs after platelets are tethered via VWF-GPIb interactions?
Platelets roll ## Footnote The rolling of platelets promotes further interactions with VWF, enhancing adhesion.
52
What stabilizes platelet adhesion to the exposed sub-endothelium?
Binding to glycoproteins additional to GPIb ## Footnote Other glycoproteins such as GPIa, GPVI, and GPIIbIIIa contribute to stable adhesion.
53
What is the primary function of secondary haemostasis?
Reinforcement of the platelet plug through the generation of a meshwork of insoluble fibrin ## Footnote This process is crucial for maintaining hemostasis after initial platelet aggregation.
54
What types of proteins are involved in the coagulation pathways?
Pro-coagulant proteins and anti-coagulant proteins ## Footnote These proteins work together to regulate the formation and dissolution of blood clots.
55
What is the coagulation cascade?
A series of reactions activating enzyme precursors to form cross-linked fibrin ## Footnote The cascade involves multiple steps where each activated component cleaves the next.
56
How many factors are involved in the coagulation cascade?
Factors I to XIII ## Footnote Each factor in the cascade is a protease that plays a specific role.
57
What are the two systems of the coagulation pathway?
Intrinsic system and extrinsic system ## Footnote These systems are taught separately for clarity in understanding coagulation.
58
What are the two groups of coagulation serine proteases?
Vitamin K dependent proteins and non-Vitamin K dependent proteins ## Footnote Vitamin K dependent proteins include II, VII, IX, X, protein C, and S; non-Vitamin K dependent include XII and XI.
59
What limits the action of tissue factor in the coagulation pathway?
Tissue factor pathway inhibitor (TFPI) ## Footnote TFPI plays a key role in controlling coagulation to prevent excessive clotting.
60
What is the major physiological anticoagulant?
Protein C ## Footnote Protein C is activated by thrombomodulin and helps degrade pro-coagulant factors.
61
What does activated Protein C degrade?
FVa and FVIIIa ## Footnote This degradation is crucial for regulating the coagulation process.
62
What is the role of anti-thrombin III in the coagulation pathway?
Inhibits other proteases: thrombin, IXa, Xa, XIa, and XIIa ## Footnote Anti-thrombin III is a key inhibitor that helps maintain balance in coagulation.
63
What is the primary process involved in tertiary haemostasis?
Fibrinolysis ## Footnote Fibrinolysis removes fibrin clots and is crucial for vascular remodeling after coagulation.
64
What is the active enzyme produced from plasminogen?
Plasmin ## Footnote Plasmin is responsible for breaking down fibrin clots during fibrinolysis.
65
When does fibrinolysis occur?
Once coagulation is initiated ## Footnote This process is essential for preventing excess fibrin formation and occlusion.

Haematology Lectures (16 decks)

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