Lecture 6: Haemostasis (PART OF HAEMATOLOGY) Flashcards
How many systems are involved in haemostasis?
5.
What are the names of the systems involved in haemostasis?
- The vascular system
- Platelets
- Coagulation cascade
- Inhibitors of coagulation
- Fibrinolytic system
What is homestasis?
A sub-branch of homeostasis concerning blood.
It is an important mechanism to minimize blood following injury, while keeping blood from clotting in vasculature.
Haemostasis is a complex interaction of 5 distinct systems.
What role does the vascular system play in haemostasis?
Vasoconstriction plays an essential role in haemostasis, modulated by adrenaline, ADP and thromboxanes, which are released by thrombocytes.
The vascular endothelial cells are a source of pro and anti-thrombotic compounds, which leads to formation of blood clots.
What role do thrombocytes perform in haemostasis?
These cells, formed by a progenitor cell called a megakaryocyte. Reference range for thrombocytes is 150-400x10^9 cells/l
Platelet granules, held in the cytosol of thrombocytes, play an important role in haemostasis: dense granules, alpha granules and lysosomes.
What role do alpha granules play in a thrombocytes function?
Alpha granules, which number around 200 per cell, contain several regulators of haemostasis, these being fibrinogen (pro-coagulant), Factor V (pro-coagulant), and Von Willebrand Factor, which serves as an adhesion molecule.
Dense granules perform what function in thrombocyte function?
Dense granules, numbering around 10 per cell also contain several key compounds including: calcium ions, ADP and serotonin, which is a potent vasoconstrictor.
What is the primary role of platelets?
The formation of a platelet plug, or a large group of thrombocytes, which acts as a temporary barrier to prevent blood loss (primary haemostasis).
What are the 4 phases of primary haemostasis?
- Platelet adhesion
- Platelet shape change
- Release of platelet granules
- Platelet aggregation
What is platelet adhesion?
(primary haemostasis)
Once thrombocytes are activated through contact with any number of physiological substances (collagen, charged surface, bacterial endotoxin, etc). These activator compounds will not normally be present until injury. (eg. charged sections of basement membrane being exposed after endothelial damage).
What is platelet shape change (primary haemostasis)
Once bound to substrate, platelets become activated and change their shape as in the prevent gaps from being present (which there would be given they remain spherical. The new ‘dendritic’ shapes will fit together more closely, filling in gaps and preventing any diapedesis or fluid leakage.
What is the release of platelet granules?
(primary haemostasis)
After thrombocytes have bound and changed shape to tightly pack together,
What is platelet aggregation?
(primary haemostasis)
What is secondary haemostasis?
What are coagulation factors?
A collection of substates, enzymes and cofactors that are responsible for the functions of thrombocytes and blood clotting.
What are the four classes of coagulation factor?
- Substrate
- Serine protease
- Cofactor
- Transglutaminase
What are serine proteases?
Enzymes that employ the use of a serine as a catalytic site amino acid.
This enzyme is prevalent in almost all vascular systems in the animal kingdom. The age of this enzyme speaks to its efficacy as a coagulation factor.
What role does vitamin K (quinone) play in blood coagulation?
Vitamin K is involved in the activation via carboxylation of several pro- and anti-coagulants. These activated factors bind calcium ions, which are hugely important in clotting.
How does Warfarin function as an anticoagulant?
A drug commonly used for the treatment of thrombo-embolic disease.
Warfarin inhibits Vitamin K- carboxylase epoxidase.
Also used as a rat poison.
How was warfarin discovered?
Due to a fungus that
What is the blood coagulation cascade?
What is the extrinsic pathway of the In Vitro model of the coagulation cascade?
Tissue factor, which is expressed on damaged endothelial cells will form a complex with both active and inactive FVII.
TF:FVIIa complex then activates FX and FXa and enters the common pathway.
((((((Relationship between factor X and warfarin here)))))
What is prothrombin time and how does it relate to the extrinsic pathway of in vitro coagulation cascade?
