Haemostasis Flashcards
What is haemostasis?
Haemostasis refers to the stoppage of bleeding.
Steps involved in Hemostasis
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- Vascular Spasm.
- Formation of platelet plug
- Formation of blood clot and clot retraction.
- Growth of fibrous tissue into the clot to form a permanent seal at the point of vessel damage.
- Removal of excess fibrous tissue.
- Repair of blood vessel endothelium.
Vascular spasm
After rupture, trauma to the vessel causes the smooth muscle in the wall to contract, instantaneously reducing blood flow from it
What are platelets?
Platelets, aka thrombocytes, are not cells but cytoplasmic fragments of extraordinarily large cells called megakaryocytes, formed in the bone marrow.
Normal Platelet Count:
130,000 – 400,000 per microliter
What comes first platelet plug or blood clot?
Platelet plug
If a blood vessel cut is small, what seals it? Platelet plug or blood clot?
Platelet plug
How long does it take for a blood clot to begin to form after severe trauma to vessels?
15-20 seconds, for minor it’s 1 to 2 minutes
Clotting takes place in ___ steps
Three essential steps:
- Formation of a complex of activated substances called thromboplastin (prothrombin activator)
- Conversion of prothrombin to thrombin
- Conversion of fibrinogen to fibrin fibers that enmesh platelets, blood cells and fibers to form clot
Which enzyme catalyzes blood clotting?
Thrombin
Functions of platelets
3 secretions, 1 formation, 1 dissolution
- Secretion of vasoconstrictors that cause vascular spasms in broken vessels
- Formation of temporary platelet plugs to stop bleeding
- Secretion of chemicals that attract neutrophils and monocytes to sites of inflammation
- Secretion of growth factors that stimulate mitosis in fibroblasts and smooth muscle and help maintain the linings of blood vessels
- Dissolution of blood clots that have outlast their usefulness
In what conditions are blood clotting factors in the blood on a normal day?
Inactive
When are blood clotting factors activated?
- When a blood vessel is broken
- When blood flow slows down.
How many clotting factors are there?
13
What are the blood clotting factors?
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- Fibrinogen
- Prothrombin
- Tissue Thromboplastin
- Calcium ions
- Labile factor (Proaccelerin)
- None
- Stable factor
- Antihaemophilic factor
- Christmas Factor (or Plasma thromboplastin component).
- Stuart-Prower factor
- Plasma thromboplastin antecedent
- Hageman Factor
- Fibrin stabilizing factor