Hemostasis Ch4 D&P Flashcards
(135 cards)
1
Q
Coagulation is the process that results in the generation of what compound? What is the ultimate job of this compound?
A
Thrombin. Which converts soluble fibrinogen into fibrin.
2
Q
What is the compound responsible for dissolution of fibrin via fibrinolysis?
A
Plasmin.
3
Q
What are the ANTI thrombotic properties of endothelium (7)?
A
Prostacyclin/PGI2 release (its a prostaglandin) > Vasodilation and platelet inhibition (via cAMP etc).
NO release > same as prostacyclin, Vasodilation and platelet inhibition.
Thrombomodulin expression > binds and inhibits thrombin and when bound this inhibits Protein C which in concert with Protein S inhibits factors 5&7 (ie it modulates thrombin and converts it from pro to anticoagulant).
Tissue plasminogen activator (tPA) > converts plasminogen to plasmin in the presence of fibrin»_space; fibrinolysis.
Heparin sulfate expression > accelerates antithrombin binding and inactivation of thrombin and factor X.
TFPI (tissue factor pathway inhibitor) > inhibits tissue factor/activated factor VII complex.
EctoADPase release > degrades locally generated ADP, which limits platelet aggregation.
REMEMBER: THe ANT PT (ie ants working out) to remember this)
4
Q
What are the procoagulant properties of endothelium (4)?
A
Tissue factor (III) synthesis. TF in combination with factor VIIa and X forms the extrinsic factor X activation complex.
VWF synthesis storage and release, which supports platelet adhesion to subendothelial collagen (synthesized and stored in Weibel-Palade bodies in vascular endothelial cells).
Plasminogen activator inhibitor/PAI-1 synthesis and release which inhibits fibrinolysis.
Endothelial damage > subendothelial exposure and enhanced plt aggregation & reduction of cell membrane associated thrombomodulin and heparan sulfates that inhibit hemostasis.
Remember: PE is better that TV.
5
Q
What on platelets serve as receptors for activation, adhesion and aggregation?
A
Transmembrane and peripheral glycoproteins within the phospholipid bilayer.
6
Q
What are the three types of granules in platelets and what does each contain?
A
Alpha > reddish, largest and most numerous and have coag and GFs, and proteins involved in platelet adhesion, aggregation and tissue repair. (Ex fibrinogen, factor V, VWF, thrombospondin, Plt factor 4, PDGF).
Dense granules > store adenine nucleotides, calcium, inorganic phosphates, serotonin (SHEMACG).
Lysosomes > acid dependent hydrolases including glycosidases, proteases, lipases.
7
Q
What is the platelet circulating lifespan?
A
five to nine days.
8
Q
Circulating platlet mass may be sequestered where?
A
Spleen. Epinephrine induced splenic contraction may increase counts. Or they may get sequestered there during congestion. BUT this does not affect platelet production.
9
Q
What regulates platelet production and how is it regulated?
A
TPO is the key in critical for all stages of megakaryopoesis. TPO is important for overall hematopoiesis. Its produced constituatively under steady state conditions (at a constant rate and degraded based on how many plts present) but may increase via marrow stroma cells during severe thrombocytopenia.
**NOTE TPO concentration is related to/inversely correlated with the mass of megakaryocytes and platelets and is NOT related to platelet number.
**Inflammatory conditions can enhance TPO production via hepatocytes, mediated by IL-6 > reactive thrombocytosis.
Other CKs involved in megakaryopoiesis and plt production include stromal cell derived factor 1, CXCR4, FGF-4 (interesting this also regs chondrodysplastic dogs), IL3, GM-CSF, stem cell factor and many other CKs.
10
Q
How do coag factors assemble on the surface of platelets?
A
Expression of phosphatidylserine.
11
Q
How does plt adhesion take place?
A
Plt exposed to subendothelial collagen, vWF > membrane glycoproteins / GPs ie GPIb-IX-V, GP-VI and alphabeta integrins like GPIIb-IIIa are key players.
GPIb-IX-V is key to gettting plts bound to collagen under high shear, it mediates transient arrest pf plts from flowin blood and weak tethering via binding VWF, tethered plts roll along and and encounted collagen fibrils and bind GPVI > activation of integrins, release of ADP > thromboxane formation. alpha2beta1 integrin txformed to high affinity state binds tightly to collagen and allows firm platelet adhesion and spreading. .
12
Q
How does platelet aggregation take place?
A
Platelet aggregation is via alpha IIb Beta3 and is txformed to high affinity state and reinforces firm plt adhesion and plt aggregation by binding fibrinogen
13
Q
How does platelet granule release take place?
A
Agonist type and concentration dependent > activation of plt phospholipases > Ca and DAG mobilization > synthesis of TXA2 > irreversible plt aggregation and release.
Release of ADP, serotonin, coag factors including fibrinogen, factor V and factor XI further enhancing plt aggregation and thrombus growth.
14
Q
What is the role of Phosphatidylserine during platelet activation?
A
Translocation to the outer membrane > facilitates Assembly of coag factor complexes > thrombin generation.
15
Q
What is the role of plts in inflammation?
A
Release of vasoactive compounds (serotonin, plt activating factor), production of CKs and interactions with Neuts.
16
Q
What is the role of plts in tissue repair?
A
Release of potent mitogens like PDGF, EGF, FGF
17
Q
Whats an important point about the size of cat platelets?
A
Its highly variable and they can be very large so on automated counts may be miscounted as RBCs and look falsely low (pseudothrombocytopenia).
Cat platelet clumping is also an issue in some counting methods.
18
Q
What is one of the most accurate ways to measure platelets on a machine?
A
Flow cytometry. The other methods are fair to good for most species, but not good with cat platelets.
19
Q
What breeds of dogs often appear thrombocytopenic and why?
A
Cavalier King Charles Spaniels due to giant platelets, which are common in this breed, being excluded from the count. Their platelet mass is normal I think.
Greyhounds generally have lower platelet counts than other dogs breeds but this is normal for them (100,000k).
20
Q
At what platelet count levels does spontaneous petechial to ecchymotic hemorrhage occur?
A
Until plt counts are below 20,000
21
Q
Two conditions where you can see thrombocytosis and in which condition is there increased risk of thromboembolic dz?
A
Counts would be higher than 800,000/uL»_space; Thrombocytosis.
Thrombocytosis associated with inflammation does not increase risk of thrombosis, BUT
Thrombocytosis associated with Myeloproliferative dz may increase risk.
22
Q
How do you estimate platelets on a blood smear?
A
8-10/100X oil > or = to 100,000 plts/ul
6-7/100X oil = 100,000/ul
<3-4 plts/100X oil = significant thrombocytopenia OR less than 1 plt/50 RBCs.
Each platelet per 100X oid = 20,000/ul. If there are plt aggregates that usually means plt counts are good.
23
Q
Platelets with vacuoles, less intense stanining and decreased granularity may mean what?
A
Platelet activation in vivo like in DIC or FeLV ( or due to poor sample handling, ie in vitro.)
24
Q
MPV is an indicator of what?
A
Average size of plts in circulation and inversely proportional to plt number.
25
Increased MPV with thrombocytopenia suggests what?
Responsive thrombopoiesis. (NOTE reticulated platelets / increased RNA, are also an indicator of this) MPV greater than 12fL indicates normal to increased megakaryocytopoiesis in the bone marrow.
26
Decreased MPV is most commonly associated with what three things?
Insufficient megakaryocytes, lack of a megakaryocyte response in the marrow and early immune mediated thrombocytopenia.
27
How is dx of present of antiplatelet antibody made (ie with ITP?)
There are assays but not that accurate; IFA labeling and Flow cytometry can be useful but don't help differentiate primary from secondary ITP. Dx of primary ITP is made by process of elimination.
28
What is the gold standard for assessment of platelet fxn and what conditions would this help dx?
Platelet aggregation.
Tests of this are useful to dx hereditary plt fxn defects like canine thrombopathia or Glanzmann thrombasthenia); or acquired disorders of plt fxn secondary to dz or drug administration (uremia, aspirin, NSAIDS etc.)
29
What does BMBT measure specifically; when is it prolonged(2); how reliable is it?
Primary hemostasis / plt status; BMBT is the most reliable clinical test for in vivo assessment of platelet function.
It will be Prolonged in thrombocytopenia. Used for animmals with NORMAL platelet counts but questionable platelet function. (ie it tests plt function testing, acquired or congenital).
COAG factor deficiencies do not prolong BMBT.
30
What does the clot retraction test measure and when is it used? In what conditions is it normal / abnormal? see diagram 4.1 pg 116
Platelet function. Just like BMBT, only used whe a known adequate platelet is present. Thrombocytopenia and admin of antiplatelet drugs will result in poor clot retraction. (think of it as clot shrinkage or tightenining, you want a nice small tight clot).
**It tests interactions between plt receptors, thrombin, fibrinogen.**
Normal in Canine thrombopathia (CalDAG-GEFI disorder, where there is an abnormal signal txduction affecting fibrinogen receptor and dense granule release), & in dogs with VWD (platelets bind VWf exposed on subendothelial collagen via GP1b).
Abnormal in Glanzmann thrombasthenia (which is a defect in GpIIb-IIIa on platelet surface that links platelets together via fibrinogen)
31
What are two tests for Von Willebrands dz?
Quantitative Elisa
| Collagen binding assay Elisa
32
How can flow cytometry be used to evaluate platelets?
To determine if plts lack major GPs like GPIIb and GP IIIa and if spp sensitive Abs are present.
Assess fxn via detection of fibrinogen binding activated platelets (via CAP 1, an antibody that detects fibrinogen bound to activated canine platelets).
33
How does plt granule release take place?
Rapid granule release depends on agonist type and concentration. Various types of agonists activate plt phospholipases which result in Calcium and DAG mobilization and synthesis of
**Thromboxane A2 > irreversible plt aggregation and release.
Stuff like serotonin, coag factors, fibrinogen etc relesed from granules enhance further plt activation and thrombus growth.
34
Key component of plt activation that has to do with thrombin generation?
Phosphatidylserine translocation to the outer membrane which facilitates assembly of coag factor complexes > thrombin generation.
35
What is von willebrands factor synthesized by? Whats its function(s)?
Synthesized predominantly by megakaryocytes and endothelial cells.
Glycoprotein needed form platelet adhesion to subenodthelial collagen and serves as a carrier for factor VIII-coagulant, it provides stability for factor VIII-coagulant in circulation.
36
What is VWD?
| What spp are affected?
a dz, inherited or acquired, that involves VWF which is a plasma protein that is needed for normal platelet function.
Its common in dogs but rare in cats, horses and cows.
Factor VIII:Coagulant activity is decreased b/c insufficient VWF to stabilize and protect the protein from degradation by proteases, but there still is some FVIII:C activity so APTT is normal.
37
What are the signs of VWD?
| How may it be treated?
Mucosal hemorrhage, prolionged bleeding from wounds, increased cutaneous bruising. A plasma txfusion or cryprecipitate that provides VWF and Factor VIII:C is necessary for treatment.
May also be treated with DDAVP which is vasopressin that causes release of preformed high molecular weight VWF multimers from Weibel_Palade bodies which works for minor surgical procedures in dogs with Type I VWD.
38
What are the different types of VWD?
Type 1 > Partial quantitative deficiency of VWF, the VWF present is normal just decreased and MOST CASES are this type. Autosomal inheritance. Severity varies.
Type 2 > Qualitative abnormalities of structure and function and its decreased in plasma. Rare. Autosomal recessive. German shorthair pointers and wirehair pointers.
Type 3 > Severe quantitative deficiency, its severe. Reduced FVIII:C but still some present so APTT is normal. Chesapeake Bay Retrievers, Scottish Terriers, Shetland sheepdogs.
Acquired VWD > When there is high shear stress like aortic stenosis etc, = unfolding of VWF and cleavage by ADAMTS13 (disintegrin and MMP necessary to prevent plt adhesion/aggregation) > into smaller multimers of VWF that aren't fxnl.
39
What are the 9 intrinsic platelet function disorders (ie defects in plts themselves)?
Chediak Higashi syndrome > abnormal plt, melanocyte and WBC granules.
Glanzmann throbasthenia > defeciency of GPIIb-IIIa integrin on plt surfaces so they can't bind fibrinogen.
CalDAG-GEFI disorders > canine thrombopathia, abnormal fibrinogen receptor exposure and impaired dense granule release.
Platelet dense granule > ADP decreased, plt count and morphology normal.
Cyclic hematopoiesis > cyclic fluctuations in plts (and neuts, retics), plt reactivity is defective and dense granules are absent.
Leukocyte adhesion deficiency type III (LAD-III) > Kindlin III deficiency or dysfxn, can't activate beta subunit type integrins.
P2Y12 > plt ADP receptor, associated with plt aggregation, binding and granule release
Scott syndrome > rare, lack of procoagulant expression on plt surface, decreased Annexin 5 binding & lack of Phosphatidylserine exposure.
Macrothrombocytopenia of Cavalier King Charles Spaniles > mutation in beta 1 tubulin genes and altered megakaryocyte proplt formation/release but no bleeding tendancies but may be miss-diagnosed with thrombocytopenia.
Remember CCCGGGLadPSM
40
What is the defect in Chediak Higashi, hows it inherited and whats the result and which animals are affected?
Autosoma recessive with lack of leukokcyte, melanocyte and plt granulation. Lack dense granules so deficient in ADP, serotonin, divalent cations etc;
diluted hair color and prolonged surfical bleeding. Mink, cattle, foxes, killer whales, mice.
In cattle mink and people linked to lysosomal trafficking regulator LYST gene.
41
What is abnormal in CalDAG-GEFI plt disorders? Whats it cause and how is it dx'd?
Inherited defect in signal txduction. Abnormal fibrinogen receptor exposure and impaired dense granule release d/t absent or dyxfunctional Calcium diacylglycerol guanine nucleotide exchange factor I, which is a signal txduction protein in the pathway leading to the conformational change in GPIIb-IIIa necessary for plts to bind fibrinogen which links plts together.
Petechaie and mucosal bleeding. Clot retraction test is normal, need plt aggregation testing to dx.
Basset hound, Eskimo, Spitz.
42
What is cyclic hematopeosis?
Autosomal recessive disorder in grey collies; cyclic fluctuations in neutrophils, reticulcyts nad platelets and melanocytes are also affected. Its a bone marrow stem cell defect that causes neutropenic episodes every 12 days with high mortality due to infection. Plt reactivity to collagen, PAF and thrombin defective. Plt dens granules absent. Clot retraction and plt adhesiveness impaired. Its a mutation in adapter protein gene AP3; has to do with export of proteins to granules.
43
What is leukocyte adhesion deficiency type III?
Disorder due to Kindlin 3 deficiency or dysfunction. Key for signal transduction and activation of beta subunit type integrins (Beta 1, 2, 3) on hematopoietic cells. Bleeding similar to Glanzmann thrombasthenia, persistent leukocytosis, susceptible to infections.
44
What are the two acquired platelet qualitative functional disorders?
Hyporesponsive platelets.
| Enhanced platelet function.
45
What are the causes of hyporesponsive platelets?(5)
Drugs (like COX inhibitors, Aspirin > acetylates COX in plts and inhibits thromboxane A2 production; ibuprofen and other NSAIDS reversibly inactivate COX and nearly all COX2 selective NSAIDs have some COX-1 activity so even the COX2's have some effect on plts..
Beta lactam antibiotics reversibly inhibits plt fxn by binding agonist receptors.
Calcium channel blockers impair plt fxn by preventing Ca mvmt across membranes.
Uremia may impair plt fxn and prolong BMBT.
DIC produce increased plasma conc of FDPs and they competitively inhibit fibrinogen.
Liver dz associate with impaired plt fxn.
Infections agents like FeLV; E. canis; paraproteinemia of plasma cell myeloma; leukemia and myeloproliferative disorders; some snake venoms.
46
What are some causes of enhanced plt function?
```
Nephrotic syndrome (multifactorial)
EPO administration
Infectious agents and parasites (FIP affects plts directly d/t endothelial cell perturbation or inflammation; heartworm dz d/t parasite products, endothelial damage and erythrolysis.)
```
47
What are the four basci mechanisms of thrombocytopenia?
Decreased production
increased consumption
sequestration
excessive loss
48
In what four situations can you get decreased platelet production or failure of plt production?
This is decreased marrow megakaryocytes with concurrent thrombocytopenia:
- Pure megakaryocyte hypoplasia, this is ab's directed against megas and can be seen with IHMA (Evans)
- Bone marrow pan hypoplasia (pancytopenia, aplastic anemia) of any cause and starts with neutropenia cause they have the shortest half life
- Myelopthisis where marrow filled with abnormal or non marrow cells
- Infectious agents like ehrlichiosis or other rickettsials associated with thrombocytpenia and FeLV, FIV, EIA, BVD (destroys marrow cells and infect stroma, decrease GF production), ASF.
49
What are causes of myelophthisis (4 causes) (and what is it)?
where marrow is occupied by other cells like in neoplasm (ie leukemia, myeloma) or other non marrow cells like
stromal proliferation in myelofibrosis or
osteoid in ostesclerosis or
disseminated inflammation in osteomyelitis.
50
Infectious agents that can trash the marrow?(7)
ehrlichiosis or other rickettsials associated with thrombocytpenia and FeLV, FIV, parvo/panleuk, EIA, BVD (destroys marrow cells and infect stroma, decrease GF production), ASF
51
What are causes of bone marrow pan hypoplasia where marrow is just empty of precursor cells?
Drugs like chemo or griseofulvin or estrogen, chloramphenicol.
Chemicals like trichloroethylene or benzene
Mycotoxins and plants (ie aflatoxin B and Bracken fern)
Ionizing radiation
FeLV or parvo
52
What are some causes (3)of platelet consumption or destruction in excess of rate of plt production?
Immune mediated ITP
Drug induced ITP
Increased activation and removal pf platelets (DIC, intravascular parasites, infections)
53
What are the types of immune mediated ITP?
- Primary Immune mediated thrombocytopenia (abs produced agains plt autoantigens like GPIIb-IIIa and GP Ib-IX and megas can also be targeted.
- With secondary its in SLE, neoplasia, infectious dz or drug administration where ag is absorbed onto plts.
- Can have vaccine induced also.
54
What are the types of drug induced thrombocytopenia?
Drug induced ITP which can be
- drug independent (ie occurs without drug admin and d/t Abs induced against normal platelet surface by initial exposure to drug and persists without presence of drug) or
- drug dependent/secondary drug induced where the drug must be administered to see the ITP.
- drugs can also cause thrombocytoepnia via non immune mechs or non targeting of platelets by causing direct agglutination and sequestration, excessive loss and removal via normal activation and coag mechs.
55
What causes sequestration of platelets?
Splenic congestion or neoplasia.
56
In what conditions does excess platelet consumption occur?
hemorrhage, trauma, rodenticide toxicosis, DIC, neoplasia
| usually only in DIC and disseminated neoplasia
57
What are three basic mechanisms or causes of thrombocytosis?
Physiologic via epi induced splenic contraction
Essential thrombocythemia (rare myeloprolif disorder)
Reactive/secondary thrombocytosis
58
What is essential thrombocythemia ET)?
Rare myeloprolif disorder that has many names and plt count is persistently high and there is variation in size shape and granulation.
Marrow megakaryocytes are increased with abnormal morphology.
Can see hemorrhage or thrombosis depending on whether plts are hyper or hypofunctional.
59
What is / what causes reactive thrombocytosis?
Increase in plt count associated with conditions other than myeloproliferative disorders this is much more common than ET.
Inflammation and Neoplasia most common causes; CKs such as IL-6, 3, 11 stimulate megakaryocyte proliferation and maturation; IL-6 may stim TPO production by hepatocytes.
Post splenectomy you can get thrombocytosis due to decreased removal or destruction by macrophages.
60
What is dysthrombocytosis?
Disordered production of plts and can be seen with megakaryocytic leukemia and myelodysplastic syndromes (which basically means cytopenias in blood hypercellular marrow, dysplastic changes in 1 or more cell lines)
Can be seen with FeLV, Chemo drugs, cephalosporin txment, inherited and acquired genetic mutations.
61
What are zymogens converted into in the coagulation cascade and what two things are required for this to occur?
Zymogens > Active serine proteases
| Requires negative charged cell membrane phopholipid surface and Calcium.
62
What are the three main coagulation factor complexes in the coagulation cascade?
1. Intrinsic factor X activation complex, AKA Intrinsic Tenase (factors 8, 9. 10).
2. Extrinsic factor X activation complex, AKA Extrinsic Tenase (factors 7, 3/tissue factor, 10)
3. Prothrombinase complex (Factors 2, 5, 10)
63
Where are coag factors synthesized?
Liver and occur in plasma as proenzymes that require activation.
64
Which factors are the enzymatic factors?
```
Factor XII (Hageman factor) and Factor XI and prekallikrien. (along with HMWK this constitutes the contact activation system.)
Vitamin K dependent factors 2 (prothrombin), 7, 9, 10.
```
65
Once vitamin K activates factors 2, 7, 9, 10 what happens?
they have a negative charge and can bind to exposed phosphatidylserine on activated platelets in the presence of Calcium - basically calcium ions allow the electrostatic interaction to occur between the coag factors and negatively charged platelet surface.
SO a memory aid is that the vitamin K dependent factors require Ca like both intrinsic extrinsic tenase (which involves 9 and 7 respectively and activate 10); and prothrombinase which is 10a and 5a activate 2.
66
What happens in the case of vitamin K antagonism?
Coag factors are synthesized without carboxylation and have inadequate functiona nd these proteins are termed "proteins induced by vitamin K absence or antagonism? or PIVKA.
67
What is factor 13 and what activates it?
Its fibrin stabilizing factor and its activated by thrombin to cross link and stablize fibrin monomers.
68
Which coag factor has the shortest half life?
Factor VII, which circulates in zymogen and active states and its 4-6 hours.
69
Whats one of the main inhibitors of clotting factors and which clotting factors does it inhibit?
antithrombin and its enhanced by heparin. Antithrombin forms complexes with and inhibits thrombin and those complexes are cleared by monocytes.
AT also inhibits factors 9, 10, 11, 12.
70
What happens to thrombin that is not inactivated by AT and not involved in an active clot?
It binds thrombomodulin, on the surface of endothelial cells and then its procoagulant activity is lost.
And thrombins substrate specificty changes from soluble fibrinogen to protein C, which is a vitamin K dependent proenzyme with anticoag nad profibrinolytic fxns.
So basically I think protein C binds it and turns thrombin off.
71
Which factors are enzymatic and which are non enzymatic and which are present in serum and why?
```
Activated enzymatic factors are NOT consumed by clotting so they are present in serum (2, 7, 9, 10, 11, 12, 13).
Enzymatic factors (made in liver and circulate) are consumed so they are absent from serum (1, 5, 8).
```
72
Which of the nonenzymatic factors are acute phase proteins?
Fibrinogen / factor 1, and factor 8, their concentration increases in plasma during inflammation or neoplasia.
73
What happens to activated factors V and VIII?
degraded enzymatically by activated protein C, which is enhanced in the presnece of phospholipid, calcium and protein S (which is cofactor for C).
74
What happens when you inactivate factors V and VIII?
Impairment of intrinsic tenase and prothrombinase and thus the anticoagulant activity of protein C, which inactivates 5 and 8.
75
Which platelet component is critical in coagulation? What is the role of calcium?
Platelet phospholipid, specifically phosphatidylserine which provides a negatively charged surface where coag factor activation is enhanced.
Ca links the negatively charged coag factors and platelet membrane phosphatidylserine residues so they are sitting their ready on the platelets.
76
Which clotting factor is NOT an enzyme that floats around the blood? What / Where is it?
Tissue factor, factor 3.
A transmembrane cell surface receptor that DOES NOT require proteolytic cleavage to become active. Its not normally exposed to plasma it just sites in cells of the adventitia around vessels and epidermal/mucosal lining cells., subendothelial fibroblasts, pericytes, endothelial cells, macrophages and monocytes.. It DOES not initiate coagulation without disruption of the endothelium. All the other coag factors circulate in plasma.
77
What can induce synthesis of TF in endothelial cells?
CKs, endotoxin, other inflammatory mediators. (but you still need disruption of endothelium for it to result in coagulation.)
78
When TF is exposed to blood what happens?
It binds factor VII / VIIa with high affinity and then activators facotr X (as Extrinsic factor X / tenase complex).
NOTE factor III / Va can also activate factor 9 of the intrinsic tenase complex.
79
What is Tissue factor pathway inhibitor, where is it found, and how does it work?
Its a lipoprotein associated protease.
Found predominately in platelets and endothelial cells.
It basically turns off FVIIa/TF and Exerts action in a two step process, first it binds activated factor X at its catalytic site and then second this complex binds FV11a/TF in a calcium dependent manner resulting in loss of FVIIa/TF activity.
80
How do anticoagulants like EDTA, oxalate and citrate work?
They prevent clotting by binding calcium
81
Which pathway generally initiates clotting in vivo?
Extrinsic, ie when TF contacts factor VII and this complex can activate factors 9 or 10.
82
Which factor is affected first with vitamin K inhibition of deficiency and why?
Factor VII d/t its short half life.
| PT may be prolonged.
83
What may happen with excessive tissue factor release as in trauma, DIC, massive necrosis, septicemia etc?
Hypercoagulation and DIC.
84
What does "contact activation" involve?
Factor 12, 11, prekallikrien, HMWK. Activated when plasma interacts with negatively charged substances in vivo (collagen, activated platelets, endotoxin) or in vitro.
The product is activated factor 11, which activates 9 and that combines with 8 to activate 10.
85
How does blood coag start and how is it sustained?
Tissue injury via extrinsic tenase activation of 9 and 10 and then sustained via intrinsic tenase which is not susceptible to TFPI and is 50 times for efficient.
86
What where is prothrombinase complex?
Factors 5a, 10a which activate factor to, just like the names says, prothrombin into thrombin. It works on the surface of platelets.
87
What are the disorders of factors in the intrinsic pathway (4)?
- hereditary sex-linked deficiency factor 9 / hemophilia B. Internal hemorrhage does occur. Carrier females don't experience hemorrhage.
- Hereditary sex linked factor 8 def:COAGULANT / hemophilia A. THE MOST COMMON INERITED COAGUOLPATHO OF ANIMIALS. VARIABLE SEVERITY OF BLEEDING. AGAIN CARRIER FEMALES DON'T HAVE CLINICAL SIGNS.
- DIC syndrome that has to do with consumption of nonenzymatic factors 5 and 8. Plts are also consumed in DIC.
- Acquired defeciency of vitamin K dependent factors, 2, 7, 9, 10
88
Under what conditions does acquired deficiency of vitamin K dependent factors occur?
Factors 2, 7, 9, 10 as in rodentacide toxicity, fat malabsorption and hepatic failure.
89
What test is abnormal initially in early rodenticide toxicity and why?
Prolongation of PT due to factor VII having the shortest half life.
90
Where is factor 5 present?
plasma and platelet alpha granules.
91
What all does thrombin activate?
Activates factors 13, 11, 8, 5 and turns fibrinogen into fibrin.(I think thats factor 1). But
thrombomodulin bound thrombin acts as an anticoagulant and activates protein C.
Thrombin also activates platelets (and is bound to platelets).
92
Which disorders affect the common coag pathway?
Factors 2, 5, 10, fibrinogena re the common ones. Disorders that only affect the common pathway are raere. Stuff lke liver dz, vitamin K antagonism and DIC are multiple hit disorders that prolong both PT and PTT.
You can get hereditary defs of factors 10 or fibrinogen and some snake venoms can activate thrombin,factors 5 and 10.
93
What are the two main disorders of anticoagulation?
1. Antithrombin deficiency (ie as in PLE, PLN, sepsis, horses with colic). DIC and liver dz can also cause AT deficiency in animals. Affected animals are predisposed to thrombosis d/t poorly regulated thrombin activity.
2. Protein C deficiency (this is described in colic horses and as a hereditary condition). these animals are predisposed to thrombosis d/t poorly regulated activity of factors V and VIII and impaired control of fibrinolysis.
94
What causes disorders of vitamin K dependent facotrs?
Fat malabsorbtion, Vitamin k rodenticide antagonism, inherited vitamin K dependent multifactor coagulopathies
95
What are the main actors in fibrinolysis?
Plasminogen and Plasmin. .
96
What activates plasminogen? Where does it and them bind?
Plasminogen is activated by kallikrein, tPA, uPA
| Plasminogen and plasminogen activators bind to fibrin within a clot.
97
Besides fibrin, what else will plasmin inactivate?
prekallikrein, HWMK, factors 5, 8, and fibrinogen.
98
What inhibits plasmin?
Plasma serine protease inhibitor alpha2 antiplasmin (alpha2AP), which complexes with and inhibits it. The complexes are cleared by macrophages.
99
What is the difference between D-dimers and FDPs?
D dimers are formed from breakdwon of cross linked fibrin and FDPs are formed from breakdown of NON-cross linked fibrin (and maybe a little cross linked fibrin).
100
How is protein C activated and what does it do?
Protien C is an inhibitor. Its activated by thrombin-thrombomodulin complex and it inhibits factors 5 and 8.
101
Besides alpha 2 antiplasmin what are four other inhibitors of plasmin?
alpha 2 macroglobulin, alpha 1 antitrypsin, AT, C1 esterase inhibitor.
102
What is TAFI?
Thrombin activatable fibrinolysis inhibitor. (its a plasminogen preventer) It inhibits fibrinolysis by cleaving exposed lysine binding sites on fibrin for plasminogen and tPA. (its a plasminogen inhibitor)
103
What are some activators of plasminogen and where are they located?
Endothelium, platelets and other cells and in plasma.
Intrinsic activator > via factor 12 (activates kallikrien that activates uPA)
Extrinsic activator > fibrin bound tPA and uPA
104
What inhibits plasminogen and where is this found
Plasminogen activator inhibitors (PAIs) from endothelium, platelets and other cells just like plasminogen activators.
105
What are five conditions that would favor hypercoagulation?
Decreased plasminogen concentration
Lack of plasminogen concentration
lack of protein C or S
Factor V mutations that result in resistance to inactivation by protein C
Excess plasminogen activator inhibitor (PAI)
106
What are two conditions that would favor hypocoagulation?
- Lack of alpha2 antiplasmin and other plasmin inhibitors may occur in DIC. Plasmin hydrolysis of factors V, VIII and fibrinogen contribute to a hypocoagulable state.
- Systemic uncontrolled plasminogen activation
107
What does ACT / activated clotting time measure and when is it prolonged (what pathway is evaluated)?
Time in seconds for fibrin clot formation in fresh whole blood after exposure to contact activator - the platelets in the blood provide the phospholipid for assembly of coag complexes.
It evaluates the intrinsic / contact and common pathways.
Prolonged when any factor is less than 10% normal, mild factor deficiencies don't affected but will prolong APTT (remember A goes with A for evaluation of the intrinsic pathway) so its not as snesitive as APTT.
108
What does a prolonged ACT mean?
- Significant and severe deficiency of coagulation factors within the intrinsic (8, 9, 11,12, HMWK, prekallikrien) or common (X, 5, 2, fibrinogen/1).
- Marked thrombocytopenia may cause prolonged ACT d/t platelets providing the phospholipid necessary for assembly of the coag complexes.)
- Coag inhibitors in the blood like heparin and citrate can also prolong ACT.
109
What is the relationship between ACT and APTT and PT?
ACT tests the same thing as APTT, intrinsic and common, and they both start with an A, but APTT is way more sensitive. Also ACT is the only clotting test to use whole blood, the others use citrated plasma.
110
What does APTT measure? If prolonged where is the defect?
Time in seconds for clot to form in citrated plasma after addition of a contact activator of the intrinsic system (which normall in vivo would be HMWK, kallekrien or collagen), phospholipid to substitute for platelets and calcium.
If prolonged = coag factor defect in the intrinsic (8, 9, 11, 12) or common (X, V, II, fibrinogen) pathways.
111
In which conditions or dzs would you see prolonged APTT?
Hemophilia A or B (def in factors 8 or 9)
hereditary factor 12 deficiency
hereditary prekallikrein deficiency
DIC
Vitamin K antagonism or def.
Liver failure
(THESE LAST THREE ARE PRETTY MUCH SEEN IN ALL TESTS)
112
How low must factors be to prolong the APTT?
Less than 30% of normal so hemophiliac (A or B) carriers/heterozygotes/females don't bleed cuase they have 40-60% of normal levels of factors 8 or 9.
Animals with VWD have decreased factor 8:C but its usually not low enough to prolong APTT, they will just have petechial hemorrhages.
113
**In early or mild rodenticide toxicity which test is prolonged first and why?
PT before APTT d/t factor VII having the shortest half life of the vitamin K dependent factors.
114
How will thrombocytopenia affect APTT? What about inflammatory dz, or administration of heparin.
It won't becuase phospholipid is added in the test to take the place of platelets cause the test uses plasma. In contrast with ACT, platelets provide the phospholipid.
Heparin will prolong APTT
Inflammation will actually decrease APTT due to increases in fibrinogen and factor VIII.
115
What are the affects of prekallikrein deficiency on APTT?
None, the activator used in the test directly activates factor 12, bypassing prekallikrein.
116
What does PT measure and how is it performed? What is it testing.
Measures the time in seconds for fibrin clot formation in citrated plasma after addition of tissue thromboplastin (a lab derived thing > factor 3/TF - not in circulation normally - plus phopholipid) and calcium. Its testing factor VII (normally circulates) and common pathway.
117
What does prolonged PT mean? In what four clinical conditions would you see it?
Defect in factor VII (extrinsic) or common (2, 5, 10 and fibrinogen/1).
1. hereditary factor VII defeciency.
2. DIC
3. Vitamin K antagonism or deficiency. (PT is prolonged first cause factor 7 has shorter half life so this test is preferred for vit K stuff).
4. Liver failure.
118
What is the preferred test for monitoring vitamin K replacement therapy?
PT because it tests factor VII, which has the shortest half life.
119
What other protein may be concurrently deficient with factor VII deficiency?
Protein C, a VITAMIN K dependent antithrombotic protein. (inhibits factors 5 and 8)
120
How will thrombocytopenia affect PT?
It will not because it uses thromboplastin as the test reagent which includes phospholipid (and factor 3).
121
What does thrombin time measure? When may it be prolonged?
time in seconds required for fibrin clot formation in citrated plasma after addition of calcium and thrombin. Essentially the entire cascade is bypassed by adding thrombin so the test depends on functional fibrinogen concentration.
Hypofibrinogen prolongs it and can occur due to excessive consumption in DIC, hereditary deficiency of fibrinogen or presence of dysfunctional fibrinogen. (dysfibrinogenemia).
122
What is the effect of heparin and vitamin K antagonism or deficiency on TT?
Heparin > prolongs TT, it promotes inactivation of thrombin.
| Vitamin K def > Does not affact TT cause thrombin is added to the test.
123
What are the most commonly inherited disorders of hemostasis in animals and how would you test for them?
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hemophilia A (factor 8 def.) and hemophilia B (factor 9 def).
Test via specific factor analysis using APTT. APTT is the only one where you can do specific factor analysis by adding the factor you think is missing back in and seeing if the test normalizes.
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124
What is the russel viper venom test?
Also called Stypven time.
It bypasses the extrinsic and intrinsic pathways and directly activates the common pathway so if prolonged would mean a deficiency of one or more factors 10, 5, 2, fibrinogen/1.
125
How do you assess fibrinogen (3)?
1. The best way is TT determination as TT is inversely proportional to fxnl fibrinogen concentration.
2. Heat precipitation is fairly crude and it may verify the presence of normal, decreased or increased fibrinogen concentration but it can tell normal from abnormal fibrinogen.
3. Estimate via calculating the difference between plasma and serum protein concentration.
126
What at FDP's? How are the measured?
Produced through plasmin degradation of both fibrinogen and fibrin (primary and secondary fibrinolysis).
Measure via citrated plasma using latex agglutination assay. It contains both fibrinogen and fibrin.
127
Whats it mean if FDP's are high (2)?
-DIC as a result of diffuse, microvascular thrombosis.
Uncompensated DIC means they are above 20ug/ml.
(compensated would range from 5-20).
-Severe liver dz with lack of clearance may also cause increase in FDPs.
128
How are D dimers produced and measured?
Plasmin mediated degradation of CROSS LINKED fibrin so it specifically indicates secondary fibrinolysis.
Measured via citrated plasma using immunologic methods.
129
What are causes of elevated D Dimers?
Variety of dz states that cause internal hemorrhage or thrombosis and is NOT always an indicator of pathologic thromboembolism.
130
What is AT and how does it work, where is it made?
Antithrombin interacts with heparin to irreversibly inactivate thrombin and other serine proteases.
Synthesized by hepatocytes.
131
What may cause AT to be low? When are animals at risk of clotting?
Decreased production in liver d/t liver failure.
Consumption like in DIC
Loss in PLE or PLN
At risk of clotting when activity is below 80% of control values
132
What are TATs?
Thrombin antithrombin complexes formed rapidly when thrombin is produced and reflect systemic activation of coagulation.
133
What is protein C specifically? When does it decrease?
Vitamin K dependent protein with anticoagulant and profibrinolytic activities. and it decreases with hypercoagulable disorders and with vitamin K antagonism.
134
What does thromboelastography (TEG) measure?
visoelastic changes that occur in blood during polymerization of fibrin, basically evaluates clot formation in whole blood.
Used to evaluate or recognize hyper and hypocoagulable states.
135
What parameters are evaluated or measured from TEG (4) tracings and what influences each of the parameters?
Time to initial fibrin formation (reaction time, R)
Time from clot initiation to predetermined clot strenght (clotting time, K)
Rate of clot formation (angle; alpha)
Maximum clot strength (MA)
see fig 4.5 pg138
R and K affected by coag factor activity
Angle affected by coag factor activity, fibrinogen conc., and platelets.
MA determiend by platelet number and fxn.
