HSF 2 - Unit 1 Biochemistry: Coagulation TBL Flashcards
what must be balanced to prevent death by bleeding or clotting?
coagulation and fibrinolysis
what are the different ways people could die due to clotting?
stroke, MI, thrombosis
what are the different ways people could die due to bleeding?
trauma, major surgery, hemophilia
what is hypercoagulation?
results in excess and or inappropriate clotting; can lead to blocking of vasculature, resulting in MI, stroke, or thrombosis; can occur when coagulation is either hyperactivated or not properly inhibited of when fibrinolysis is inhibited or not properly stimulated
what is hypocoagulation?
results in an inability to properly form clots, and results in excessive bleeding; fibrinolysis is either hyperactivated or not properly inhibited or coagulation is inhibited or not properly stimulated
what are the inherited disorders in clotting?
hemophilia A, B, factor V Leiden, vonWillebrand disease
hemophilia A
X-linked deficiency in factor VIII
hemophilia B
X-linked deficiency in factor IX
factor V Leiden
mutation in factor V such that it cannot be inactivated by active protein C
vonWillebrand disease
deficiency in vonWillebrand factor (vWF), most common inherited clotting disorder, vWF is required for primary plug formation, and it stabilizes factor VIII in the serum; can be developed late in life and may not necessarily be due to an inherited defect
what are the acquired disorders in clotting?
Vitamin K deficiency, liver disease, antiphospholipid antibody syndrome, vonWillebrand disease
Vitamin K deficiency
rare because of intestinal microbes’ production of vitamin K, but can occur in newborns or in combination with medical treatments or conditions that severely alter gut microbiota
liver disease
several of the soluble clotting factors, proteins C and S, are produced by the liver, so diseases that may impair the liver’s production of these factors will result in clotting abnormalities; sometimes hypo- and sometimes hypercoagulation
antiphospholipid antibody syndrome
an autoimmune disorder in which antibodies attack phospholipids, this can damage cells in the blood or the lining of the blood vessels, subsequent release of phospholipids and other contents to the serum triggers clotting
what does a platelet count consist of?
part of a CBC, includes hemoglobin concentration and WBC count; normal levels are 150,000-450,000 platelets per microliter
what does PT measure? how is it performed?
PT= prothrombin time; measures rate of clotting by the extrinsic and common pathways, and is determined mainly by the amount of prothrombin in the plasma; oxalated blood is treated with thromboplastin, which contains excess Ca2+, phospholipids, and tissue factor, and clotting times is measured, normal time = 11-14 seconds
what does a sample vial from a PT test contain? why?
citrate, oxalate, or EDTA; all of these are able to chelate Ca2+, and thus inhibit coagulation of the sample prior to analysis
what is an INR?
international normalized ratio; it is a standardized method of PT so we can compare with other labs; each lab runs own control samples (control PT) and uses that with the ISI value (specific for each lot of thromboplastin) to determine INR; = (patient’s PT/control PT)
what is ISI?
international sensitivity index; usually around 0.9
what is a normal INR value?
0.8-1.2
what is a PTT? what is a normal result?
partial thromboplastin time; measures the rate of clotting by the intrinsic and common pathway; oxalated blood is treated with excess Ca2+, phospholipid, and a nucleating surface such as kaolin and clotting time is measured; normal = 30-42 seconds
what is the activating agent in a PTT?
has a high negative charge density, and mimics the effects of exposed subendothelial collage, thus stimulating the intrinsic pathway, can be varying things
what are the deficiencies that PT/INR and PTT are sensitive to?
deficiencies in the common pathway: factors X, V, II, and I
how are serum fibrinogen and clotting factor concentrations be determined?
typically a follow-up to PT/INR and aPTT in order to determine the exact deficiency/excess that is causing the problem; D-dimers are soluble in the serum and are elevated in the serum following intravascular coagulation
an injured blood vessel will initially ______, which … then …
contract; restricts the blood flow; platelets begin to aggregate at the site and form a hemostatic plug
what do platelets signal after gathering at the site of injury? what happens?
initiate the clotting cascade, in which a fibrin network is formed and this is the secondary hemostatic plug
when does the fibrin network begin to develop? what does it require?
during primary hemostatic plug formation, and requires the activation of prothrombin to form thrombin, which then activates fibrinogen to form fibrin
when does primary hemostatic plug formation begin?
when circulating platelets adhere to exposed subendothelium
what do platelets contain?
granules that are released upon platelet activation; hold calcium, ADP, serotonin, heparin antagonist, fibrinogen, some clotting factors, platelet derived growth factor, vWF
what will COX do?
produce thromboxane A2 (TrxA2) after platelet activation
what does PAR1/PAR2 do?
binds activated thrombin
what does GPIa do?
binds collagen
what does GPIb do?
binds vWF
what do GPIIb/GPIIIa do?
binds fibrinogen and vWF
what does the binding of plateletis to subendothelium result in?
platelet activation and aggregation
thrombin binds to _____ and activates…
PAR1/PAR and activates a Galphaq signaling pathway; the resulting increase in intracellular calcium activates phospholipase A2 as well as granule release
binding of ______ to collagen causes…
GPIa/IIA to collagen causes platelets to swell and produce pseudopods
binding of _____ to vWF causes…
GPIb to vWF increases GPIIb-IIIa exposure on plasma membrane surface
ADP binds…
P2Y12, stimulating production of more GPIIb/IIIa
platelet activation and aggregation is ______, facilitates …, and is the target of …
autocatalytic, wound closure, anti-platelet drugs
what do ADP and TxA2 have in common?
both have autocatalytic functions; they stimulate further activation and aggregation of platelets
what are TxA2 and serotonin?
vasoconstricters, released from granules
what facilitates formation of the secondary hemostatic plug?
calcium, clotting factors, fibrinogen, and heparin agonist that are released from granules; platelet derived growth factor will stimulate repair of the endothelium
what do anti-platelet drugs do?
inhibit platelet activation/aggregation; aspirin inhibits COX, preventing TxA2 and plavix is an antagonist of the P2Y12 (ADP) receptor
how is fibrin produced?
upon proteolytic cleavage of fibrinogen by thrombin and subsequent covalent cross-linking by factor XIIIa
fibrinogen is a _____ of ______, linked by…
dimer; heterotrimers; disulfide bonds
what does cleavage by thrombin release?
fibrinopeptides A and B
most clotting factors are…
zymogens that are activated by proteolytic cleavage
what do the zymogen forms of clotting factors contain?
binding domains that attract them to the area of endothelial damage, and/or growth factors that will facilitate endothelial repair
glu-rich regions in clotting factors
get modified by vitamin K-dependent carboxylase: carboxylation at the gamma carbon of glutamate forms gamma-carboxuglutamyl (Gla) residues
what is Gla?
an excellent chelator of calcium, and allows the negatively charged proteins to interact with negative PL
what happens to vitamin K during the carboxylation reaction?
gets oxidized; must be reduced by vitamin K epoxide reductase and vitamin K reductase
what factors contain Gla regions?
X, IX, VII, II, proteins C and S
what can prevent carboxylation of proteins and thus act as anticoagulants?
vitamin K antagonists, such as warfarin and dicoumarol
how does exposure of collagen trigger the intrinsic pathway?
exposure to highly negatively charged surfaces, including collagen and glass
what is a soft clot?
after thrombin cleaves fibrinogen to form fibrin, this aggregates to form this clot
how do we strengthen the clot?
covalent cross-linking mediated by FXIIIa (activated by thrombin)
what is FXIIIa?
a transglutamidase
what does thrombin activate?
factors V, VII, and XI and thereby accelerating the rate of clot formation; also stimulates platelet aggregation, thus further promoting secondary clot formation
what is thrombomodulin? where is it expressed?
when complexed with thrombin activates protein C, which forms an active complex with protein S to cleave FVa and FVIIIa, thus slowing the clotting cascade; expressed on endothelial cell surfaces, since thrombin’s affinity is high for this it is removed from the plasma
what are serpins?
serine protease inhibitors; a group of naturally occurring inhibitory proteins
how many serpins are there? what do they do?
8; inhibit either coagulation or fibrinolysis
what is an important example of a serpin?
antithrombin III; irreversibly inactivates thrombin, as well as a few other clotting factors; its activity is enhanced x10000 in the presence of heparin, which is normally present in very small amounts in the plasma and is used clinically as an anticoagulant
why does blood not clot on intact vascular endothelia?
- Negatively charged platelets are repelled by the highly glycosylated, negatively charged endothelial surface
- Endothelial cells secrete both prostaglandin I2 (PGI2), aka prostacyclin, and nitric oxide, which are vasodilators and powerful inhibitors of platelet aggregation.
- PGI2 synthesis is stimulated by thrombin – feedback inhibition - Endothelial cells present both thrombomodulin and heparin sulfate (HS) on their luminal surface. (HS is a weak mimic of heparin.)
what is a non-thrombogenic surface?
The normal endothelial vascular cell lining neither activates coagulation nor supports platelet adhesion
how is a clot dissolved?
fibrinolysis; plasminogen, a plasma protein, has a high affinity for fibrin and is incorporated into the fibrin clot during coagulation; proteolysis of plasminogen by tissue plasminogen activator (tPA) or urokinase (U-PA) produces plasmin, a protease that cleaves fibrin, as well as several clotting factors
what is tPA synthesized by? how are rates of synthesis modified?
vascular endothelial cells, and urokinase is produce by most tissues; physical stress, hypoxia, and a number of small molecule regulators increase the synthesis and release of tPA and urokinase
what can recombinant tPA and ______ be used to treat?
streptokinase; treatment of MI and stroke
what is fibrinolysis inhibited by?
plasminogen activator inhibitor 1, and by alpha2 - antiplasmin
what is PAI-1 and what does it do?
plasminogen activator inhibitor 1, inhibits the activation of plasminogen; is inactivated by active protein C (which is activated as clot formation ends)
what does alpha1-antiplasmin do?
inhibits free, but not clot-bound plasmin; particularly important for inactivation of any plasmin present in the plasma
