Cardiovascular Flashcards
Platelet biochemistry
What is the action of prostacyclin on platelet activation/ adhesion/ aggregation in undamaged areas?
Inhibition
Prostacyclin inhibits platelet activation/ adhesion/ aggregation in undamaged areas
Platelet biochemistry
Damage to the endothelium of blood vessels causes what to be exposed?
Collagen
Platelet biochemistry
What is adhesion?
Platelets binding to exposed collagen
Platelet biochemistry
Which receptors/ intermediate molecules help during initial adhesion?
During intial adhesion GP1B receptors on platelets bind to the intermediary Von Willebrand factor (VWF) on the exposed collagen
Platelet - GP1B - VWF - Collagen
Platelet biochemistry
Which receptors/ intermediate molecules help during stable adhesion?
GPVI receptors on activated platelets help them bind to collagen directly
Platelet - GPVI - Collagen
Platelet biochemistry
How do platelets adhere to each other? (Mention receptors/ intermediate molecules)
Platelets adhere to eachother using GP2b/3a receptors and fibrinogen as an intermediate
Platelet - GP2b/3a - Fibrinogen - GP2b/3a - Platelet
Platelet biochemistry
The binding of platelets to collagen releases the contents of their secretory vesicles via exocytosis.
Which molecules are released?
- Thromboxane A2
- Thrombin
- ADP
Platelet biochemistry
Where is thromboxane A2 derived from?
Arachidonic acid is converted into Prostaglandin H2 by the COX 1 enzyme.
Prostaglandin H2 is converted into Thromboxane A2.
This is done in platelets.
Platelet biochemistry
What is the action of Thromboxane A2?
It causes vasoconstriction and further platelet acitvation and aggregation.
Platelet biochemistry
Where is thrombin derived from?
Thrombin (a.k.a factor 2a) is the activated version of Prothrombin (factor 2).
Prothrombin is a protein that comes from the liver.
Platelet biochemistry
What is the action of thrombin?
Thrombin binds to PAR1 and PAR4 (both are receptors on platelets).
This activates platelets and induces further thrombin release (positive feedback).
It also leads to the release of ADP from electron dense granules.
Platelet biochemistry
What happens specifically when thrombin binds to PAR1?
Intracellular stores release Ca2+ which results in the inhibition of translocase and activation of the scramblase protein.
This causes the aminophospholipids present on the inner membrane of the platelets to be expressed on the outer membrane.
This leads to the assembly of prothrombinase and allows for prothrombin to be converted into thrombin.
Platelet biochemistry
What is the function of ADP (released from electron dense granules)?
Binds to P2Y1 and P2Y12
P2Y1- leads to further activation of platelets
P2Y12- leads to further aggregation of platelets
Platelet biochemistry
What are the effects of platelet activation?
Platelets change shape from smooth discoid to spiculated with psuedopodia
The number of GP2b/3a receptors increase (leading to more platelet aggregation) and their affinity to fibrinogen also increases.
Platelet biochemistry
What are the different types of granules in platelets?
Electron dense granules
Alpha granules
Platelet biochemistry
What molecules do electron dense granules release?
Ca2+
ADP/ATP
Serotonin
Platelet biochemistry
What molecules do alpha granules release?
Fibrinogen
VWF
Platelet derived growth factor
Platelet biochemistry
What does serotonin do?
Stimulates vasoconstriction
Platelet biochemistry
Which two molecules stimulate vasoconstriction?
Thromboxane A2
Serotonin
Platelet biochemistry
What is the primary haemostatic plug?
The primary hemostatic plug is the initial platelet-rich clot that forms at the site of a vascular injury, temporarily stopping blood flow.
Platelet biochemistry
Put these in order and summarise them:
Aggregation, Injury, Activation, Adhesion
- Injury- Vasoconstriction via endothelin release
- Adhesion- Platelets binding to exposed collagen
- Activation- Pseudopodia and granule release
- Aggregation- Platelets binding to platelets using GP2b/3a receptors and fibrinogen
Platelet biochemistry
Where is prostaglandin H2 derived from?
Arachidonic acid is converted into prostaglandin H2 via COX1 and COX2 enzymes
Platelet biochemistry
What can prostaglandin H2 be converted into?
Thromboxane A2 or Prostacyclin
Platelet biochemistry
How do Thromboxane A2 and Prostacyclin differ?
Thromboxane A2 is a vasoconstrictor and promotes platelet activation
Prostacyclin is a vasodilator and inhibits platelet activation/ adhesion/ aggregation
Clotting cascade
What is the clotting cascade?
A series of events that results in a stable blood clot that stops bleeding
Clotting cascade
What is the difference between the intrinsic and extrinsic pathways?
The intrinsic pathway responds to spontaneous, internal damage of the vascular endothelium, whereas the extrinsic pathway becomes activated secondary to external trauma.
Clotting cascade
Explain the extrinsic pathway
When the endothelium is damaged the endothelial cells release tissue factor.
Tissue factor along with factor 7a activates factor 10 into 10a.
Clotting cascade
Explain the intrinsic pathway.
Exposed collagen activates factor 12 into 12a.
Factor 12a activates factor 11 into 11a.
Factor 11a activates factor 9 into 9a.
Factor 9a activates factor 8 into 8a.
Factor 8a, along with factor 5a, converts factor 10 into 10a.
Clotting cascade
Explain the common pathway
Factor 10a converts prothrombin (factor 2) into thrombin (factor 2a).
Thrombin converts fibrinogen (factor 1) into fibrin (factor 1a).
Clotting cascade
What coagulation factors does the liver produce?
Every factor except 3, 4 and 8.
Clotting cascade
Where is VWF produced?
Liver