Hematostasis Flashcards
What are the 6 steps of hemostasis?
- vascular constriction
- formation of platelet plug (primary hemostatic plug)
- formation of a blood clot as a result of blood coagulation (secondary hemostatic plug)
- clot retraction
- fibrinolysis
- growth of fibrous tissue into the blood clot
What are the two causes of vasoconstriction? Which vessels do each act on?
- local myogenic spasm: circular smooth muscle
- local factors from traumatized tissues and blood platelets: smaller vessels
The first reaction contraction of circular smooth muscles is called? What is this type of contraction reducing?
- Myogenic contraction
- reduce the flow of blood from a ruptured vessel
What are the by product vasoconstrictors from the platelet plug formation?
Thromboxane A 2 (TXA 2) and serotonin (5-HT)
What are some facts about platelets?
- no nuclei
- can’t reproduce
- contractile protiens are: actin, myosin, thrombosthenin
- ER and Golgi: make enzymes and store calcium
- factor XIII
- cell membrane have glycoprotein coat
What are 5 types of platelet disorders?
- thrombocytosis
- thrombocytopenia
- platelet function defects
- inherited
- acquired
What are 3 examples of inherited platelet disorders?
- von willebrand disease
- bernard-soulier syndrome
- glanzmann thrombasthenia
What are examples of aquired platelet disorders?
- certain drugs like nsaids, PCN, ASA, or heparin
- idiopathic thrombocytopenic purpura
- chronic myeloproliferative disorders
Platelet plug formatiom includes what 3 A’s?
Adhesion, activation, aggregation
Where is the von willebrand factor found? What is it? What does it do?
- megakaryocytes and in alpha granules
- its a glycoprotien made by endothelial cells
- it binds to the platelet receptor glycoprotein (Gp Ib)
What triggers a conformational change in the platelet receptors?
Adhesion
What 3 things promote platelet aggregation?
-ADP, serotonin, TXA2
What inhibits clotting by decreasing the release of TXA2? Its an inhibitor of what?
- aspirin
- aspirin is an inhibitor of cyclooxygenase
What forms bridges between platelets? What step of the primary hemostatic plug does this happen?
- Fibrinogen
- aggregation
What is a clot?
Semisolid mass composed of platelets and fibrin
When a vessel is ruptured, what is activated? What does it override when its activated?
- Procoagulants
- overrides anticoagulants
When does a clot start to develop? Within how many minutes does the opening of the vessel get filled with a clot? When does the clot retract?
- 15-20 seconds clot develops
- 3-6 minutes
- 20min to 1hr
What factor require the liver to be functioning? What vitamin is required as well?
- Factor II and IIa, VII and VIIa, IX and IXa, and X and Xa
- vitamin k
What are the names for factor I, Ia, II, IIa?
- I: fibrinogen
- Ia: fibrin
- II: prothrombin
- IIa: thrombin
Warfarin is an anticoagulant drug. What is its antidote, or reverses its function?
-vitamin k
What is central to the coagulationc cascade?
Thrombin
What is required for clot retraction?
Platelets
What two things increase the levels of circulating t-PA?
Catecholamines and bradykinin
What are two paracrine factors of anti-clotting mechanisms? What do they do?
- prostacyclin (PGI-2): vasodilation and inhibits platelet activation
- nitric oxide: through cGMP inhibits platelet adhesion and aggregation
What pathway does PT measure? Which does PTT measure? What are their functions?
- PT: extrinsic, assess anticoagulant effect of warfarin
- PTT: intrinsic, ability to convert fibrinogen to fibrin clot
What type of vitamin is vitamin k? What symptoms would you see if absorption of this is defected?
- Fat soluble
- steatorrhea, greasy stools, bloating, gas
What do platelets release when there is a wound? What action does it cause?
- TXA2 and serotonin
- increase platelet aggregation and vasoconstriction
What is the lifespan of platelets? When they die, how are they removed from the body?
- 8-12 days
- by macrophages in the spleen
What are released from endothelial cells that stimulate muscle contraction?
Endothelins-1 (ET-1)
What are platelets?
Fragments of megakaryocytes
What are the two types of platelet granules? What are in each?
- alpha granules: procoagulant factor 5, fibrinogen, von willebrand factor, PF4, growth factors (tissue growth factor, PDGF)
- dense granules: ADP, serotonin, calcium
What granule and aspect of this granule plays a role in the recruitment and activation of platelets?
- Dense granules
- ADP
What glycoprotien receptor binds to collagen?
Glycoprotein Ia/Ib
Which glycoprotein receptor binds to von willebrand factor? What disease is linked tothe lack of this receptor?
- glycoprotien Ib/IX
- Glanzman’s thromboasthenia
Which glycoprotien receptor binds to fibrinogen? If there is a lack of this receptor, what disease can occur?
- glycoprotien receptor IIb/IIIa
- Bernand-Soulier syndrome pseudo-vWD
What do endothelial cells release to INHIBIT platelet aggregation and relax smooth muscle? What is the process that it does this?
- Prostacyclin
- prostacyclin activates platelet adenylate cyclase, increases cAMP, decrease intracellular Ca, and inhibits platelet activation
What is a potent inducer of platelet aggregation and vasoconstriction? Where are they released from?
- TXA2
- platelets
Injury of the endothelial exposes collagen. That exposure of collagen causes what and why?
- Adhesion of platelets to the endothelium
- glycoprotien receptor Ia/IIa seeks the exposed collagen to link to
What happens in the activation step of platelet plug creation?
- adhesion causes an intracellular signalling cascade leading to exocytosis of platelets to go to the injured site
- activates both the alpha and dense granules
If a patient is bleeding with low platelet count, what step of coagulation will not work?
Second step: primary hemostatic plug
Whats the difference between a clot and thrombus?
- clot: semisolid mass composed of platelets and fibrin
- thrombus: blood clot in a vessel that has ability to move
Between procoagulants and anticoagulants, which dominates?
Anticoagulant
What factors are released in the intrinsic pathway? Extrinsic? What factor do both pathways meet at?
- intrinsic: factors 12, 11, 9, 8
- extrinisic: factor 7 and tissue factor
- factor 10
What type of cells clear the activated clotting factors once its no longer needed?
Kupffer cells of the liver
