hemostasis II

what is thrombopoietin (TPO)?
the factor for hematopoietic stem cells to go toward toward megakaryocytes
how do megakaryocytes produce platelets?
endomitosis, the nucleus is replicated but the DNA remains intact and starts sloughing off cells -> platelets
where is TPO produced?
in the bone marrow, liver and kidney. (EPO produced in the kidney)
what is the receptor for TPO?
CMPL
how are platelets activated?
ADP is released by many platelets and received by P2Y1 and P2Y12 which then through signal cascades changes the conformation of GpIIb/IIIa causing it to bind fibrinogen
what does platelet receptor GpIb/V/XI bind?
vWF and endothelium
what is glanzmann thrombasthenia?
a deficiency in GpIIb/IIIa, which keeps the platelets from aggregating b/c they have to bind to fibrinogen to bind to each other. (a similar effect would be seen with afibrinogenemia)
what is bernard soulier syndrome?
a deficiency in GpIb; therefore platelets cannot adhere to the subendothelium. (similar to vWD, where platelets cannot adhere to the endothelium)
what is the specific amino acid sequence both GpIb and GpIIb/IIIa bind to in fibrinogen and vWF?
RGD: arginine, glycine, aspartate
what is an additional function of vWF?
carrying/protecting factor VIII – so a vWF is similar to hemophila A
what is ADAMTS-13?
a metalloprotease that cleaves vWF (a large multimeric protein produced by endothelial cells), which is itself made in the liver. ADAMTS-13 is the major regulator for vWF size and provides protection against uncontrolled platelet adhesion.
how can a deficiency in ADAMTS-13 cause thrombocytopenia? what is this condition called?
an ADAMTS-13 deficiency is called thrombotic thrombocytopenia purpura and in this case, the platelts are all adhering to large vFW fragments on the subendothelium/aggregations and are not present in general circulation
what causes ADAMTS-13 to cut vWF into smaller pieces?
high shear stress
what two granules do platelets have?
alpha (PF4, vWF, etc) and dense granule (ADP etc)
what is grey platelet syndrome?
large platelets that do not have alpha granules
where do prostaglandins come from?
phospholipase A2 cuts arachidonic acid from the #2 position, COX on platelets make the prostaglandin TXA2 while COX on endothelial cells will make PGI2(prostacyclin). (TXA2 is one of the most potent vasoconstrictors known)
if you eat more omega-6 FA’s such as arachidonic acid, what eicosanoids will be produced in greater number?
series 2 prostaglandins (TXA2/PGI2), and series 4 leukotrienes
if you eat more omega-3 FA’s such as EPA (eicosapentanoic acid), what eicosanoids will be produced in greater number?
series 3 prostaglandins (antiinflammatory), series 5 leukotrienes
what omega # is linoleic acid? is there a correlation with cardiovascular disease?
omega 6; of which there is a INVERSE correlation with cardiovascular disease with (it may decrease the risk of CVD)
what omega # is linolenic acid? what is it said to do?
omega 3; which should decrease the amount of pro-inflammatory cytokines (TNF-alpha, IL-1, and IL-6) and also decrease CVD
what happens to platelet membranes that PLA2 has cleaved all the arachidonic acid from?
the phospholipids missing an arachidonic acids “flip out” causing the surface to be negatively charged – allowing them to ready for coagulation
what is found on the surface of platelets when activated?
once activated, integrins form a “surface raft” which help the platelet by allowing for stronger surface interatction/signalling events
what are platelet microparticles (PMP)?
these are tiny particles released from cells (including platelets) during apoptosis that have a negative charge which is pro-coagulant/thrombogenic. tissue factor is also found on these microparticles in encrypted form.
what is the shape change that occurs when platelets are activated?
round to discoid
what is the platelet cytoskeleton composed of?
actin and myosin which help tighten up the shape of activated platelets
what are 2 diseases causing defects in platelet adhesion?
bernard soulier disease which is a lack of GpIb/IX/V and vWF deficiency
what are 2 diseases causing problems in platelet aggregation?
glanzmann’s (missing GpIIb/IIIb) or afibrinogenemia
what is wiskott-aldrich?
X-linked mutation in WASP, causing hereditary thrombocytopenia
what is an example of a storage pool disease?
grey platelet syndrom
what usually causes TTP? what is the platelet cut off where it has to be considered?
ADAMTS-13, but also infection/autoantibodies. 140,000 is the platelet cut-off
what is essential thrombocythemia?
a rare myeloid neoplastic disorder where there are too many platelets (platelets are abnormal in size and aggregate quickly and inappropriately), pts w/this tend to bleed slightly more. it can be treated with warfarin long term
what does the blood coagulation cascade start with?
the extrinsic, then later it shifts to the intrinsic
what part of the coagulation cascade is associated with the phospholipid surface, platelets, and blood vessels?
the intrinsic pathway
what part of the coagulation cascade is associated with phospholipids and tissue factor?
the extrinsic pathway
what part of the coagulation cascade is associated with thrombin and fibrin clot formation?
the common pathway
what is the key to activation of the coagulation system?
thrombin, which provides feedback activations
what are the 3 things that can activate factor XI in the intrinsic pathway?
XII, VII and thrombin
what 2 things activate factor IX?
factor XI and VII
what 2 factors activate factor X?
VII and IX
what complex shifts the coagulation cascade to the intrinsic system?
tissue factor pathway inhibitor which inhibits the complex of factor VII, tissue factor, and factor X. increased thrombin concentration then activates the intrinsic side through feedback loops
where is tissue factor found in it’s inactive state?
tissue factor is an (internal/external) integral membrane protein usually expressed by extravascular cells (esp heart, lungs, testes, uterus, placenta) and encoded on microparticles. it is separated by a primary hemostatic barrier on blood vessels, but following injury it rapidly activates blood coagulation
what is the structure of fibrinogen? where does thrombin cleave?
a mustache where alpha/beta/gama are at each end, gamma points down in the middle where the mouth would be and the alpha/beta chains point up into where the nose would be <- where thrombin cleaves, and once i does = fibrin
what is a fibrin soft clot?
when thrombin cleaves the center alpha and beta chains, this spot gets sticky and it binds to the ends of other fibrin molecules non-covalently
how do soft fibrin clots become hard?
factor XIII crosslinks (ligase between a lysine and a glutamine) adjacent fibrin molecules after being activated by thrombin
what are the procoagulant properties of thrombin?
platelet activation (via integrin), activates factors V, VIII as well as XI and VII, it converts fibrinogen to fibrin and activates factor XIII
what is the lupus antiphospholipid antibody?
people with this have no (or very minor) bleeding disorder, however, their blood is slow to clot in a test tube and they will have a prolonged PTT (b/c antibodies block the phospholipids which are part of the test). in severe cases, this can be treated with oral anticoagulants
how do you determine if someone has phospholipid antibodies?
russel’s viper venom activates factor X directly (bypasses blood clotting cascade to test factor X)
how do thrombin and endothelial cells inhibit thrombosis?
thrombin is inactivated by antithrombin III, and endothelial cells provide heparin to potentiate this
how do endothelial cells inactivate factors X and VII?
via tissue factor pathway inhibitor
how do endothelial cells inhibit platelet aggregation?
release of PGI2, NO and ADP phosphatase
how do endothelial cells activate the fibrinolytic system?
by releasing tissue plasminogen activator
how is protein C activated? what does it do?
protein C is activated when thrombin binds to thrombomodulin as expressed by endothelial cells at the correct time. this complex activates protein C which then inactivates factor V and VIII
what does tissue factor pathway inhibitor inhibit?
extrinsic factor X activation, which needs the complex to act
what causes factor V leiden? what happens as as result?
arg->gln mutation. the factor V leiden mutation leads to protein C resistance by factor V, leading to more clotting than usual (5-7x increased risk of thromboembolism)
what are 2 inhibitors in the thrombolytic system?
plasmin activator inhibitor and plasmin inhibitor <- both will allow the clot to remain/continue to form
what are some thrombolytic therapy agents? how are they administered?
streptokinase, urokinase, t-PA (tissue plasminogen activator, alteplase) and recombinant t-PA. these are delievered by catheter to the area of the clot except with pulmonary embolisms (b/c it will dilute the drug and break up other possibly necessary clots)
what kind of protein are factors XII, XI, X, II, VII, plasmin, C1, elastase, and trypsin? what inactivates these?
serine proteases which have 3 AAs in their active site; aspartate, histadine and serine. these are inactivated by serpins which are produced in the liver, circulate the blood and suicide inhibit serine proteases and clear them from circulation
what are serpins/hemostatic inhibitors that block clotting?
ATIII, C1inh, alpha1 protease inh
what are serpins/hemostatic inhibitors that block fibrinolysis?
plasminogen activator inhibitors (PAI), and plasmin inhibitors
what are serpins/hemostatic inhibitors that shift reactions?
TFPI shifts from extrinsic to intrinsic
what does heparin do (2 things)?
binds to antithrombin III and enhances its inhibitory activity by changing its conformation and folding out and drawing targets in
what are benefits of LMW heparin?
higher anti Xa/IIa activity ratio (inhibits thrombin generation, not just thrombin activity), it has a longer half life, it is more uniform/predictive, it may not react with protamine as an antidote, and it has a ****lower association with HIT
are there any benefits of unfractionated heparin?
it may be better for obese, elderly, renally insufficient, and pregnant pts
does LMW heparin have less of a chance of causing HIT?
yes
what is HIT?
a highly prothrombotic, hypercoagulable disorder (not hemorrhagic), caused by exposure to heparin in complex with PF4 on the platelet surface, resulting in an immune rxn -> leading to a systemic thrombotic response (venous 4x more common)
what is hirudin?
a direct thrombin inhibitor that is unaffected by platelet factor 4 and inactivates thrombin bound to fibrin -> more predictable anticoagulant response (derived from leeches)
what can snake venoms do in terms of coagulation?
snake venom can initiate consumption of coagulant substances and; produce a protease that directly hydrolyses prothrombin, directly clots fibrinogen, activates platelets (kills small mammals by overclotting) and activates endothelial cells to produce a plasminogen activator (fibrinolysis)
what happens in DIC?
in disseminated intravascular coagulation, there is consumption of all the platelets and coagulation factors resulting in extreme bleeding somewhere else