Lecture 5.2 - Haemostasis

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Questions and Answers

What is the primary function of antithrombin III in haemostasis?

To activate platelets

To enhance fibrinolysis

To inhibit thrombin formation (correct)

To promote vasoconstriction

Which of the following is NOT a function of endothelial cells in haemostasis regulation?

Activating coagulation cascade (correct)

Enhancing fibrinolysis

Producing heparins

Inhibiting platelet activation

What is the primary function of tissue plasminogen activator (tPA) in fibrinolysis?

To convert fibrinogen to fibrin

To inhibit thrombin formation

To activate plasmin from plasminogen (correct)

To activate factor VIII

Which of the following coagulation factors is NOT involved in the intrinsic pathway?

Factor VII Signup and view all the answers

What is the primary clinical feature of Von Willebrand disease?

All of the above Signup and view all the answers

Which of the following is a consequence of excessive thrombin formation?

Thrombus formation Signup and view all the answers

What is the primary function of factor XIII in the coagulation cascade?

To stabilize the fibrin clot Signup and view all the answers

Which of the following is NOT a component of the primary haemostasis?

Coagulation cascade Signup and view all the answers

What is the primary function of prostacyclin (PGI2) in haemostasis regulation?

To inhibit platelet activation Signup and view all the answers

Which of the following is a characteristic of bleeding disorders?

All of the above Signup and view all the answers

Which of the following bleeding disorders is inherited in an autosomal recessive manner?

Haemophilia C Signup and view all the answers

Which step of haemostasis is primarily affected in Haemophilia A and B?

Step 3: Coagulation cascade Signup and view all the answers

What is the normal platelet count in a healthy individual?

150-400 x 10^9/L Signup and view all the answers

What is the characteristic feature of bleeding in thrombocytopenia?

Prolonged bleeding time, normal PT and APTT Signup and view all the answers

Which of the following is a cause of thrombocytopenia due to decreased platelet production?

Bone marrow infiltration by malignancy Signup and view all the answers

What is the characteristic bleeding pattern seen in thrombocytopenia?

Small vessel bleeding, appearing as petechiae Signup and view all the answers

Which of the following is a cause of thrombocytopenia due to dilutional thrombocytopenia?

Massive blood transfusions Signup and view all the answers

What is the minimum platelet count required for spontaneous bleeding to occur?

Less than 20 x 10^9/L Signup and view all the answers

What is the primary site of production of clotting factors in the body?

Liver Signup and view all the answers

Which of the following is a cause of disseminated intravascular coagulopathy (DIC)?

Sepsis Signup and view all the answers

What is the purpose of warfarin in the context of bleeding disorders?

To prevent clot formation in patients at high risk of thrombosis Signup and view all the answers

Which laboratory test is used to measure the extrinsic pathway of coagulation?

Prothrombin time (PT) Signup and view all the answers

What is the name of the condition characterized by an abnormal factor V that is not deactivated, resulting in thrombosis?

Factor V Leiden Signup and view all the answers

Which laboratory test is used to detect thrombus formation, such as deep vein thrombosis (DVT) or pulmonary embolism (PE)?

D-dimer Signup and view all the answers

Study Notes

Haemostasis

Haemostasis is the process of stopping blood loss after injury
It consists of two parts: primary haemostasis (platelet plug formation) and secondary haemostasis (fibrin clot formation)

Primary Haemostasis

Platelets are derived from megakaryocytes and have a discoid shape with no nucleus
Platelets contain glycoproteins that interact with specific ligands
Primary haemostasis involves the interaction of platelets, subendothelium, and fibrinogen
Platelet granules are present in three types: alpha, dense, and lysosomal granules

Platelet Adhesion

Endothelial injury exposes subendothelial matrix proteins to circulating blood
Vasoconstriction occurs first, reducing blood loss, with nitric oxide helping in the process
Von Willebrand factor (vWF) is released by endothelial cells and is important for platelet adhesion
Initial platelet adhesion involves the interaction of vWF and the GP1b receptor on the platelet surface

Platelet Activation and Shape Change

Binding of platelets to vWF triggers their activation, causing:
- Thromboxane generation (vasoconstrictor)
- Granule release (containing ADP, PAF, and fibrinogen)
- Activation of GPIIb/IIIa receptor (allowing platelets to bind to fibrinogen)
- Platelet shape change (swelling, forming extensions, and spreading across the subendothelium)

Platelet Aggregation

Nearby platelets are recruited and become activated
Following activation of GPIIb/IIIa, platelets begin cross-linking
Nearby platelets bind to each other via the GP IIb/IIIa receptor, mediated by fibrinogen, and form a plug

Secondary Haemostasis

Secondary haemostasis forms a stable mesh network and a permanent thrombus
It involves a series of reactions involving coagulation factors (enzymes made by the liver) to produce thrombin
Thrombin cleaves fibrinogen and forms fibrin

Coagulation Cascade

The coagulation cascade has three pathways: extrinsic, intrinsic, and common
The extrinsic pathway is activated by tissue factor (TF) released by endothelial cells after external damage
The intrinsic pathway begins when factor XII becomes activated after exposure to subendothelial collagen
The common pathway results in the formation of thrombin, which cleaves fibrinogen to form fibrin

Fibrin Clot and Fibrinolysis

Fibrinolysis is the process of breaking down a fibrin clot
The central protein involved in fibrinolysis is plasminogen, which is converted to its active form, plasmin
Plasmin works by converting insoluble fibrin into soluble degradation products
Fibrinolysis is an important process to prevent excessive clotting

Bleeding Disorders

Bleeding disorders involve a deficiency in clotting factors or proteins important in the coagulation cascade
Examples of bleeding disorders include:
- Von Willebrand disease (deficiency in vWF)
- Haemophilia (deficiency in factor 8, 9, or 11)
- Thrombocytopenia (low platelet count)

Thrombophilia

Thrombophilia is a predisposition to thrombosis due to inherited or acquired defects of haemostasis
Examples of thrombophilias include:
- Factor V Leiden
- Antithrombin deficiency
- Protein C or protein S deficiency
- Antiphospholipid syndrome

Laboratory Testing

Laboratory tests used to diagnose bleeding disorders include:
- Prothrombin time (PT)
- Activated partial thromboplastin time (APTT)
- Platelet count
- Bleeding time
- D-dimer (detects thrombus formation)

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Description

This quiz covers the basics of haemostasis, including the composition of blood clots and the role of endothelium in regulating haemostasis. Learn about platelet aggregation, coagulation, and fibrinolysis.