Haemostasis Flashcards
What is haemostasis?
a process to prevent and stop bleeding, meaning to keep blood within a damaged blood vessel (clot?)
What happens if the haemostatic mechanism is hyperactive?
Unwanted blood clots (thrombi) may occur
Can block blood vessels and cause tissue death
What are the 3 main steps of haemostasis
1) Contraction of injured blood vessel
2) Formation of platelet plug
3) Coagulation of blood
What is the texture of the blood vessel lining?
Smooth and invert (unreactive)
What happens to the blood vessel smooth muscle when injured and why?
It contracts to reduce blood flow
During platelet plug formation, where does the platelet attach to?
The damaged endothelial layer
What protein factor is platelet plug formation facilitated by?
The von willebrand factor
What does the von willebrand factor do?
forms a bridge between collagen and platelets
Which structure reinforces the platelet plug?
a fibrin lattice
When does a fibrin lattice occur?
When the plasma protein fibrinogen is converted to fibrin (by the enzyme thrombin)
Where are many coagulation factors formed and what nutrient is needed for their synthesis?
Liver
Vitamin K
Which enzyme converts fibrinogen to fibrin
Thrombin
Name 3 signs that indicate a clotting problem
Primary haemostatic defect (bleeding more than usual):
Sometimes no clinical signs Nose bleeds Vaginal/ penile bleeding Petechiation Ecchymosis Haemorrhages in the skin Mucous membranes
What is thrombin converted from?
Prothrombin - an inactive precursor in the blood
How does thrombin convert fibrinogen to fibrin?
Through cascade/ chain reactions - with the help of factor X (prothrombinase) - clotting factors
It is triggered by vessel wall contraction
What is Fibrinolysis?
The process which dissolves the blood clot once the injury is healed
Why does a fibrin lattice need to form?
To reinforce the platelet plug and ensure it does not give way under pressure
How do platelets stick to each other?
They release an active substance that makes their surface sticky
Where is prothrombin found?
In the blood
What is prothrombin?
A precursor to thrombin found in the blood
Why does thrombin need to convert fibrinogen to fibrin?
So fibrin can form a fibrin lattice to reinforce the platelet plug
What is fibrin?
a protein
What happens if haemostasis does not work properly?
Catastrophic bleeding can occur even after small injury
What happens during the coagulation cascade?
Clotting factors (coagulation factors) prompt reactions that activate more coagulation factors
initiated by extrinsic pathway and intrinsic pathway
