Bleeding Flashcards
What is haemostasis?
The arrest of bleeding, involving the physiological processes of blood coagulation and contraction of damaged blood cells.
What happens if blood fails to clot outside of vessels?
Bleeding disorder
What is it called when blood clots inside a blood vessel?
Thrombosis
Haemophilia is a bleeding disorder in which blood bleeds into…?
Muscles and joints
Which bleeding disorder is X-linked and only affects males?
Haemophilia
What is the difference between haemophilia A And B?
Haemophilia A: deficiency in Clotting factor 8
Haemophilia B: deficiency in clotting factor 9
What is the use of von Willebrands Factor (VWF)?
Acts as a bridge/ mediator between platelets and collagen fibres when endothelial cells of the blood vessel are disrupted.
Platelets have receptors for VWF and VWF binds to collagen
I what kind of inheritance is von Willebrands Factor (VWF) disease?
Autosomal dominant inheritance
Why is liver disease often associated with bleeding and prolonged prothrombine time (PTT)?
The liver is the site of synthesis of coagulation factors and fibrinogen
What is the most common cause of liver disease?
Alcohol
Vitamin K is needed for the correct synthesis of coagulation for which coagulation factors?
II, VII, IX, X (2,7,9,10)
Remember 1972
How does aspirin affect platelet function?
Inhibits platelet aggregation
What does heparin and warfarin inhibit?
Vitamin k
What is Disseminated Intravascular Coagulation (DIC)
When small blots develop throughout blood stream, clotting small blood vessels (micro vascular thrombosis) This increase in clothing leads to the deficiency of clotting factors and platelets since they’ve been used up in the formation of the microvascular thrombosis.
Why does a blood vessel constrict and release endothelium-1 when damaged
This temporarily slows the flow of blood in the affected area and the opposed endothelial surfaces that are pressed together induced a stickiness that glued them together
Name the two interdependent processes that stops bleeding
Formation of platelet plug
Blood coagulation
To cause platelet amplification and aggregation, what receptors do ADP bind to?
P2Y1 and P2Y12
What happens when ATP binds to P2X1 receptor?
Platelet amplification
Define platelet activation and aggregation
Activation: change of platelet shape from smooth discoid you speculated (spiky) with pseudopodia, therefore increasing its surface area
Aggregation: when new platelets adheres to old ones, therefore rapidly producing a plug in the vessel
What releases and synthesizes Thromboxane A2
Platelets
What does thromboxane A2 do?
Causes activation, aggregation and release of secretory contents of platelets
Also causes vascular smooth muscle of blood vessels to contract
What is the role of fibrinogen
Forms bridges between aggregating platelets
Why does the platelet plug not expand continuously throughout the blood vessel?
Adjacent undamaged endothelial cells:
- synthesize and release prostacyclin aka prostaglandin I2 (PGI2) which inhibits aggregation and is a vasodilator.
- release nitric oxide which inhibits adhesion, activation and aggregation and acts as a vasodilator
Name the two pathways of blood coagulation and state the difference between the two.
Intrinsic: Everything needed for it to happen is in the blood
Extrinsic: Cellular element outside of blood is needed for it to occur
What protein polymer does the blood clot mainly consist of?
Fibrin
List in the order the steps of the Intrinsic Pathway of blood coagulation
- Factor XII activated to XIIa when in contact with certain surfaces eg. collagen fibres
- Factor XIIa catalyses the activation of factor XI to XIa
- XIa activates factor X to become Xa with VIII as a cofactor
- Xa converts prothrombin to thrombin
- Thrombin converts soluble fibrinogen to insoluble fibrin which secures the clot and builds it up
Aside from factor XIa acting as an enzyme for the activation of factor X, what is the cofactor involved in this reaction?
VIIIa
Most cases of haemophilia (excessive bleeding) comes from the genetic absence of which plasma protein?
VIII
Thrombin contributes to the activation of…?
Platelets,
XI and VIII (Intrinsic),
V and X (indirect as Va acts as cofactor for X activation)
What starts the extrinsic pathway of blood coagulation?
Tissue factor of subendothelial cells of damaged vessel binds to factor VII to activate the clotting factor and form a complex
What is the type of activation that activates Factor XII in the intrinsic pathway?
Contact activation
What is the only cell type that does not have tissue factors?
Endothelial cells
What are the steps of the extrinsic pathway of blood coagulation?
- Tissue factors of subendothelial cells of the damaged blood vessel bind to VII, activates it and forms a complex
- The complex formed on the membrane of the tissue cell catalyses the activation of X and IX in the intrinsic pathway. These both lead to the activation of X to Xa
- Xa converts prothrombin to thrombin with VIIIa as a cofactor
- Thrombin catalyses formation of fibrin from fibrinogen
Why is blood coagulation considered the dominant haemostatic defense?
It supports and reinforces the platelet plug and solidies blood that remains in the wound channel
What is blood coagulation/ clotting?
The transformation on blood into a solid gel called clot/ thrombus
