Flashcards in Zlotnik 4 Deck (22):
What is hemostasis and what are the mechanisms?
Hemostasis: prevention of blood loss
1) vascular constriction (fast)
2) formation of platelet plug (fast)
3) formation of a blood clot (coagulation)
4) growth of fibrous tissue to close a vessel hole permanently
What is structure of a blood vessel?
Inner endothelial ring, outer vascular smooth muscle
-contractile response of vascular smooth muscle
-sensory impulse from traumatized muscle stimulates smooth muscle by thromboxane A2 release (from platelet) (fast)
-can close arterioles and small arteries
Describe platelet aggregation (plug)
-platelets become sticky and start to plug the injured vessel (fast)
Describe blood coagulation (clot)
-fibrin strands start to appear where the plug is
-forms a stable clot = thrombus
-the clot contracts (happens slowly, but is more permanent)
Megakaryocyte -> platelet (thrombocyte)
stimulated by IL3, thrombopoietin, GM-CSF, stem cell factor
Diff between serum and plasma?
Serum has coagulated, removed a lot of coagulation proteins already
-plates are 2-4 microns, no nuclei, lifespan of ~10 days, old platelets macrophages in the spleen
-cant divide or make proteins
-hyalomere (outside), microtubules that maintain shape
-granulomere (inside) contains granules
Besides forming thrombus (platelet plug), what are other roles of platelets?
Blood coaguation: phospholipids on surface of platelets important for this
Platelet granule fxn: platelet granules release prohemostatic and anti-hemostatic substances
What is involved in platelet adhesion?
-integrins (integral membrane receptor)
GP IS GLYCOPROTEIN RECEPTOR
ex. GP lalla: binds collagen (beneath the vascular bed)
GP lbIX: binds von Willebrand factor (on vascular smooth muscle)
RECEPTOR BINDING ACTIVATES PLATELETS
What are some granules released by platelets and what are the effects?
"rest" spherical shape..."activated" stellate shape
-serotonin -> vasoconstriction
- ADP -> amplification (activate other platelets)
PAF, vWF, Pfact4, TXA2 also released
What does Ca2+ do in platelet activation? How is phospholipase A2 activated? Other players?
Ca2+ increased in activation
-activates phospholipase A2
COX1 (cyclooxygenase 1) IMPORTANT
release of thromboxane A2 (activates other platelets in feedback amplification)
What does aspirin do?
Inhibits platelet activation and aggregation
-inhibits COX1 irreversibly
non steroidal anti inflamm drugs (NSAIDs) such as ibuprofen and naproxen are REVERSIBLE COX inhibitors
What is the problem with tylenol (acetaminophen, paracetamol)?
-most common cause of medication related cause of liver toxicity
What is GP LLbLLLA?
Fibrinogen receptor, is exposed during activation
-allows one platelet to bind to another by having both bind to fibrinogen
How do anticoagulants work?
They can bind to receptors (ie. Plavix binds to ADP receptor) thus preventing ACTIVATION of the platelet
How long can a small dose of aspirin (<100 mg) last?
Effect can last for days (antithrombotic)
What is normal platelet count? What is thrombocytopenia? Characteristics? Types?
normal: 150k - 400k/ul of blood
Thrombocytopenia: decrease in platelets; <150k/ul of blood
primary thrombocytopenic purpura: unknown cuase
secondary: due to known cause: aspiran overdose, leukemia, dengue fever
What test for thrombocytopenia?
Tourniquet test: use blood cuff to elevate blood pressure, if >20 petechiae in area of 3 cm diameter, then thrombocytopenia
Bleeding time: normal 2-6 min
Platelet versus coagulation disorder?
See slide 25 on lec 4
What is thrombocytosis
platelets is >400k /ul of blood
-develop thrombotic (clotting) events
-stroke, heart attack, etc
-causes vessel occlusion and gangrene