semester 2: L6: Blood- Mechanisms of Homeostasis Flashcards
What is Haemostasis?
process of stopping bleeding
keep blood within the damaged vessel
What are the three steps of Haemostasis?
Vasoconstriction
Formation of platelet plug
Blood coagulation
What occurs in endothelium damage?
Collagen becoming exposed is the trigger for the platelets to come
The platelets activate and come to the site
The platelets aggregate and activation of Coagulation occurs
Thrombin is formed, which works with fibrinogen to form fibrin
Fibrin is a mesh which is constructed to form fibrin polymers
it is then retracted (ripped apart) forming fibrin fragments
What are platelets?
Produced in the bone marrow from megakaryocytes
Cytoplasmic extensions on the cell surface break off
anucleate
Smaller than red blood cells, colourless
Cytoplasm contains mitochondria, SER,
Granules (dense, alpha and lysosomal)
what role does serotonin and 5-HT receptors play in platelet aggregation?
vasoconstrictor
platelet activation and aggregation
What is platelet activating factor involved in?
platelet activation and aggregation converts memb phospholipids to thromboxane A2 thromboxane A2 vasoconstrictor increases capillary permeability inflammation also from monocytes and neutrophils
How is ADP involved in platelet activation?
from platelet mitochondria
platelet activation and aggregation
Vasoconstriction and platelet plug formation
How is the platelet plug formed?
all the factors involved in the activation of platelets lead to the production of loose platelet clumping, which causes vasoconstriction at the same time
This results in the temporary haemostatic plug
The temporary haemostatic plug is formed before the definitive haemostatic plug
What is the von Willebrand factor?
primary function is to bind to other proteins, mainly factor VIII (8)
What is Weibel palade?
These are bodies in endothelial cells that release von Willebrand Factor
Why don’t all platelets clump?
This is due to Nitric oxide
Nitric Oxide inhibits the platelet activation,
It also is a potent vasodilator
Which factors is Calcium involved in helping?
Factors; VII (7),
X (10),
IX (11),
II (prothrombin)
How does the Extrinsic Pathway of coagulation begin?
Set off by the tissue factor released in the endothelial cells, due to endothelial damage
How does the Intrinsic Pathway of coagulation begin?
Set off by the exposure of collagen due to endothelial damage, in which activates factor XII (12)
Where do the two pathways meet?
At Thrombin
What does Thrombin convert Fibrinogen into?
Fibrin Polymers
What do factors 2, 7, 9, 10 contain?
Contain vitamin K-dependent g-carboxyglutamate (Gla) residues
How do zymogens become active factors?
This is through the binding of calcium to the Gla residues
How do factors V, and VIII (8) become activated?
By thrombin
How does factor II change when activated?
Inactive factor II is Prothrombin, and when activated by Xa it becomes Thrombin
What things have to come together in order to activate factor 2?
Ca2+, factor Va, factor Xa and prothrombin
Prothrombinase complex
What does the prothrombinase complex combine with in order to drive Thrombin?
Complexes with Phosphatidylserine (PS) and Phosphatidylinositol (PI) on platelet surface
How does factor V play a part?
If body senses low concentrations of thrombin, factor V will activate
If the body senses there is enough thrombin concentration, Factor V will be cleaved
What exactly converts prothrombin to Thrombin?
Factor Xa and Factor Va and Ca2+ ions
