Homeostasis and Treatment of Coagulation Disorders Flashcards
hemostasis
normal (regulated) activation of blood coagulation system in response to vascular damage (stop blood flow)
coagulation
blood clot
problems with hemostatic defects
- thrombosis - blockage of vein/artery resulting from inappropriately activated/persistent blood clot
- hemorrhage - loss of blood from arteries/veins due to injury or aneurysm
hemostatic systems
- coagulation factors: plasma proteins (serine proteases) - involved in blood clot formation after injury
- platelets: cell fragments form primary plug - involved in blood clot formation + release mitogenic factors - aid in repairing damaged blood vessels
- fibrinolytic system: plasma proteases: remove fibrin clots once repair to damaged blood vessel occurs
heparin
natural compound = inhibit blood clot (inhibits cleavage of factors)
a form = active form
inactive form = zymogen
activated by cleavage
more selective for 2a than 5a
clotting pathways
extrinsic pathway = activated in response to tissue injury
V11a (7) tissue factor + phospholipid (PL) + Ca2+
convert X >Xa (10)
intrinsic pathway: glass surface activates XII (12) activating XII (12), XI (11), IX(9) IXa + VIIIa + PL + Ca2+ = activate X
common pathway: Xa (Va + PL + Ca2+)
convert prothrombin (II) > prothrombin (IIa)
= converts fibrogen > firbrin monomers
= XIIIa converts > fribin polymer
functional assessment of coagulation
prothrombin time (PT)
- tests extrinsic + common pathways
- addition of tissue factor, calcium, and PL
- 10-13 secs
activated partial thromboplastin time (aPPT)
- tests intrinsic + common pathways
- addition of activating surface, Ca2+, and PL
- 35-55 secs
(reproducible - store blood for future use)
whole blood clotting time
- whole blood drawn into glass tube (activating surface)
- tests for disorders in any aspect of coagulation
- 2-3 minutes (done there and then)
inherited disorders of coagulation
hemophilia A - deficiency/defect factor VIII (8)
hemophilia B - deficiency factor IX (9)
treatment for hemophilias
plasma factor concentrates factor 8+9
- purified from pooled human plasma donors
- risk of transmission of infectious disease (HIV/Hepatitis)
hemophilia a = RECOMBINATE
- recombinant form of factor 8
- produced in CHO cells
hemophilia b = BENEFIX
- recombinant production of factor 9
- produced in CHO
anticoagulants
used to prevent occurrence/progression of deep vein thrombosis/pulmonary embolism
carefully monitored to avoid overdose with hemorrhage
effects may be increased with liver disease + antiplatelet drugs
intravenous anticoagulants
HEPARIN
- activate antithrombin III
- extracted from animal tissues
- direct inhibitor of serine protease of intrinsic/common pathway factors
- rapid onset of action - monitored by aPPT
- low molecular weight = more reproducible
- rare se: osteoporosis/hypoaldosteronism/elevated K+
oral anticoagulants
WARFARIN
- inhibitor of intrinsic/common pathways
- vitamin K antagonist
- interferes with activation of 9,10,7,2
- used for long-term anticoagulant therapy
- teratogenic
- monitored with PT
PT measurements are normalized
. PT - measured in tandem with patient sample
. patient PT converted to International Normalized Ratio (INR) (dividing patient clotting time by standard clotting time)
. dose of warfarin adjusted to give INR between 2-4
side effects of warfarin
risk of intracranial bleeding with INR>4
skin necrosis associated with genetic protein C/S deficiency
teratogenic - first trimester
drugs that interact with warfarin metabolism by mixed-function oxidase (cytochrome P450)
disulfiram
fluoxetine
clopidogrel
bile acid resins
roles of platelets in hemostasis
- platelets are activated by contact between glycoprotein receptors on platelet surface + collagen exposed during cell wall injury
- platelets adhere to damaged site + provide PL for the formation of 10a + 11a
- aggregation of platelets further stimulated by thromboxane + ADP
- platelets form nucleus for clot formation
- clot = cluster of platelets cross-linked by fibrin
platelet aggregation + activation
adhesion of platelets to damaged surface
release of ADP
synthesis of thromboxane
expression of aggregation receptors: glycoprotein 2b/3a
crosslinking of platelets by binding of firbin to glycoproteins receptors
antiplatelet aggregation agents
ASPIRIN = inhibits Cox 1 blocking synthesis of thromboxane
long-term effect = platelets cannot synthesize new cox-1
prevent atherosclerotic plaques, pulmonary embolism, strokes
contraindicated if patient is being treated with anticoagulants/liver disease
//others: TXA2 R antagonists GP IIB/IIIa expression inhibitors/receptor antagonists
CLOPIDOGREL
competes with ADP for binding to ADP receptor on platelets = prevents expression of glycoprotein R for fibrin
inactive when administered, requires metabolism by cytochrome P450
fewer problems with GI irritation than aspirin
Optical Aggregometry
measures the quantity of light passing through a sample of platelet-rich plasma (PRP) using platelet-poor plasma as a reference
Addition of a platelet agonist to PRP causes
platelets to aggregate & fall out of solution producing an increase in % transmittance of the sample
Impedance Aggregometry
Measures the electrical current passing between
two electrodes placed in whole blood.
Addition of a platelet agonist causes platelets to
aggregate on the electrode surface resulting in a decrease in current between the electrodes
Quantitative Platelet Disorders
• Thrombocytosis*: (>700,000 platelets/µL), can
be caused by malignancies of the megakaryocyte lineage, splenectomy, anemia or rebound from thrombocytopenia
• Thrombocytopenia: (<50,000/µL), can be caused by autoimmune diseases, transfusion reactions, radiation, chemotherapies, extracorporeal circulation, and heparin
Treatment of Platelet Disorders
• Thrombocytosis:
HYRDOXYUREA + APIRIN + APLHA INTERFERON
(side effect: nausea, diarrhea, seizures)
• Thrombocytopenia:
CORTICOSTEROIDS / PLATELET RICH PLASMA
The Fibrinolytic System
- Initiated after coagulation occurs
- Active agent is plasmin, a serine protease = degrades fibrin and factors II, V, and VIII
- Plasminogen is inactive precursor of plasmin
- Endogenous plasminogen activators include tissue plasminogen activator (tPA) and kallikrein
Fibrinolytic Drugs
• Activate plasminogen to form plasmin
STEPTOKINASE
• Used primarily to treat acute myocardial infarct (MI) and prevent a 2nd heart attack (must be used within 12 hrs of original MI to be effective)
