Hemostasis Flashcards
Hemostasis
Steps body takes to limit blood loss - clot formation
What are platelets derived from?
Megakaryoctyes
Platelets are ____ of megakaryocytes
Cell fragments
Another name for platelets?
Thrombocytes
What is the normal range of platelets?
150K - 450K
Less than ____ platelets is lethal
10K
What things do platelets contain?
- Actin, myosin, mitochondria
- Dense core granules and alpha granules
- Cox1 - generates thromboxane A2
- Serotonin
What types of granules do platelets contain?
Dense core and alpha granules
What neurotransmitter do platelets contain?
Serotonin
What molecule regulates platelet production?
Thrombopoietin (TPO)
What produces Thrombopoietin?
Kidney and Liver
What receptor does Thrombopoietin bind to?
C-MPL
What cells contain C-MPL receptors?
Megakaryocytes/platelets/other hematopoietic stem cells
When TPO binds to C-MPL receptor on megakaryocytes, what results?
Formation of platelets
What happens to TPO when there is a high number of platelets?
It is mostly bound to C-MPL receptor and then gets internalized and degraded by megakaryocytes and platelets
What happens to TPO when there is a low number of platelets?
It is mostly free and NOT bound to C-MPL
What controls the secretion of Thrombopoietin?
Itself and platelets
What are the steps to Hemostasis?
- Vascular spasm (vasospasm)
- Formation of platelet plug
- Clot formation
What platelet factors are involved in vasospasm?
Serotonin and Thromboxane A2
Why don’t platelets adhere to each other?
Their NEGATIVE CHARGES
Adhesion of platelets to the site of injury is initiated by the activation of?
Platelet receptors
What receptor on platelets stimulates platelet adhesion through its activation?
GP 1b/1a
What does GP 1b/1a bind to?
Von Willebrand Factor (vWF)
After GP 1b/1a binds vWF and its activated, what does this cause?
Release of platelet contents:
- Release of ADP, serotonin, thromboxane A2, Fibrinogen, vWF
Release of platelet contents causes?
Activation and aggregation of more platelets
What receptor on platelets does ADP bind?
P2Y12
Once fibrinogen is released, it binds platelet receptors to do what?
Bridge platelets together and forms the plug
Release of what from activated platelets causes the plug to form?
Fibrinogen
What is important in the formation of a clot?
Thrombin
Thrombin takes fibrinogen to?
Fibrin
Fibrin polymerization and contraction of the clot requires?
Calcium
What does Aspirin inhibit?
Clot formation by inhibiting release of more thromboxane A2
What does Clopidogrel (plavix) inhibit?
P2Y12 receptors on platelets to block further platelet activation
When the platelets release ADP, serotonin, and thromboxane A2, what does that do?
Those molecules go on to bind more receptors on platelets which activates them and causes more platelets to aggregate at the injury site to form the platelet plug
Aspirin and plavix reduce clot formation by blocking molecules that?
Stimulate more activation and aggregation of platelets
