Flashcards in Thrombosis Deck (23):
Describe the typical structure of an artery or arteriole
Endothelial cells lining the lumen
Surrounded by basal lamina (made by endothelial cells)
Smooth muscle cells surround basal lamina
Interstitial collagen fibres (collagen in connective tissue between structures) surrounds this
What is the difference between serum and plasma?
Plasma contains clotting factors
Serum is plasma without clotting factors
Where are clotting factors mainly produced?
Describe the clotting cascade (amplification sequence) when there is damage to a tissue
1) Damage exposes interstitial collagen fibres and tissue factor
2) TF reacts with various clotting factors, finally producing Xa-Va
3) Promthrombin is converted to thrombin
3) Thrombin causes soluble fibrinogen to to polymerise to form insoluble fibrin
4) Fibrin cross links leading to coagulation
How is the clotting cascade (amplification sequence) initiated?
1) Trauma ∴ blood leaks out of blood vessel
2) Clotting factors in contact with interstitial collagen fibres ∴ activated
3) Tissue factor is released from smooth muscle cells
4) TF binds to clotting factor ∴ initiates clotting cascade
Describe the structure of most clotting factors and how most are activated
Many CF are serine proteases
They have serine Amino Acid section and enzyme section
- CF cleaves next CF in cascade
- Producing active CF and redundant fragment
How are platelets produced?
Produced in bone marrow
From cell called a megakaryocyte
(large cell with many nuclei)
Platelets synthesised in the cell and bud off as fragments from cytoplasmic extensions
Describe how platelets work as coagulants
1) Trauma ∴ exposure of platelets to interstitial collagen
2) Platelets clump together and try to form a bridge to close gap in the blood vessel
What is coagulation?
Solidification of blood
1) Thrombus formation
2) Clot formation
What is the difference in the composition of a thrombus and a clot?
Thrombus - Mesh network of fibrin strands + platelets
Clot - Mesh of fibrin strands + RBCs
What are the conditions for the formation of a clot and a thrombus? How are the different?
Thrombus occurs when there is flowing blood
Clots occur when the blood flows out and become stationary
What feature of platelets allow thrombus formation in flowing blood?
They have molecules on their surface that allow adherence to interstitial collagen
What is the function of coagulants?
Haemostasis - stopping bleeding
What ways does the body try to minimise/stop bleeding?
- Clot/thrombus formation
- Vessel vasoconstriction of damaged vessel
Describe how clot and thrombus formation are used together to achieve homeostasis
Clots form in the space around the vessel to fill the void of the wounded tissue
Thrombus forms to seal the gaps in the blood vessel
After a wound is successfully plugged, what will happen?
Angiogenesis - capillaries grow into clot
It becomes granulation tissue
Blood supply provides oxygen/nutrients etc and keeps GT alive
What is ischaemia?
Lack of blood flow to tissues
Can happen if thrombus blocks blood flow
Will lead to hypoxia (lack of oxygen)
Aside from ischaemia & hypoxia, what negative effect cam thrombus formation have?
Blocks blood flow ∴ stagnant blood behind it ∴ clotting
Lead to a mixture of clot and thrombus
Under normal circumstances, once a blood vessel is repaired, then the clot and thrombus are removed.
How is excess thrombus and clot removed?
Fibrinolytic system present in blood
Fibrinolytic = breaks down fibrin
This stops thrombi from propagating
How does the fibrinolytic system work?
Consists of a plasma protein called plasminogen
This is converted to plasmin
Plasmin breaks down fibrin strands
What does Virchow's triad describe?
Factors that cause abnormal clotting/thrombosis which can lead to many diseases
What is Virchow's triad?
Abnormalities of vessel wall
Abnormalities of components of the blood
Abnormalities of vessel flow