10a- Intro to Hemostasis- Normal Hemostasis Review Flashcards
What things are involved in primary hemostasis? What is the goal of primry hemostasis?
Vasculature
blood flow
platelet count function
extracellular matrix proteins
leads to a platelet plug
What things are involved in secondary clotting? what is the goal?
coagulation factors
goal is a fibrin clot
What are the initial steps after vascular injury?
- arteriolar vasoconstriction
- reduces blood flow
- mediated by endothelin
- Exposure of subendothelial Von Willebrand Factor (vWF) and collagen
What are the 4 main steps of primary hemostasis?
- Platelet adhesion
- Patelet actiavtion
- shape change
- granule
- recruitment
- aggregation
What hapens durnig platelet adhesion?
binding of platelet glycoprotein 1b (Gp1b) to vWF and exposed collagen
There are 2 phases of platelet activation. shape change and granule release. What happens during the shape change phase of primary hemostasis?
- increasing their surface area
- move negatively cahrged phospholipids to the surface (for binding Ca)
- conformational change in platelet glycoprotein
There are 2 phases of platelet activation. shape change and granule release. Whatis released during the granule release phase?
- alpha granules
- fibrinogen, clotting factors, vWF, platelet factor 4, platelet derived growth factor, fibronectin
- Dense granules granules
- ADP, ATP, Calcium serotonin, epinephrine
- Stimulate platelet activation
- Then Recruitment!
What happens during the aggregation phase of primary hemostasis?
- Gp IIb/IIIa binds fibrinogen, forming bridges between platelets
- initial wave is reversible
- thrombin stimulates irreversible platelet contraction, and conversion of fibrinogen to insoluble fibrin
What are the 4 steps of secondary hemostasis?
- Phospholipid complex expression
- tissue factor
- thrombin activation
- firbin polymerization
What is the goal of secondary hemostasis? What is the end result?
Goal: generation of thrombin (F2a)
End Result: fibrin clot
What do the enzymatic reactions of secondary hemostasis require?
- phospholipid membranes of platelets (negative surface)
- inactive substrate (factors)
- calcium
- active enzyme (activated factor)
- positive feedback (F2a)
Where are clotting factors made? What form do they circulate in? WHat are they dependent on?
- produced in the liver hepatocytes
- exception F8
- circulating in inactive, functional form (ACTIVE forms produced during)
Which factors are viatmin K dependent?
F2, F7, F9, F10
Protein C and S
Negatively charged clotting factors are localized to ______, which has been attracted to the negtaively charged ___________ of the platelet
Negatively charged clotting factors (F2, F7, F9, F10) are localized to the Ca, which has been attracted to the negatively charged phospholipid surface of the platelets
Efforts to control process to a limited surface
What is the goal of secondary hemostasis? What happens during secondary hemostasis?
- Thrombin generation is the goal
- Conversion of fibrinogen to firbin
- stabilization of firbin (F13a)
- Amplification of clotting cascade via positive feedback (FXI, F5, F8)
- potent platelet activator
- Activates endothelium
- platelet inhibition (NO, PGI2)
- Fibrinolysis initiation (tPA)
- Anticoagulation
- Proinflammatory effects
What is the purpose of fibrinolysis? what happens?
Limit the size of the thrombus and dissolution
- tPA (endothelium actiavtes plasminogen into plasmin
- plasmin breaks down fibrin, producing fibrin degradation products (ie D Dimers)
- alpha-antiplasmin inactivates free plasmin
What are the natural anticoagulants for normal hemostasis?
- Endothelial acitvation and release of mediators (PGI2, NO, ADP) which inhibit platelets
- actiavtion of thrombomodulin, which leads to activation of Protein C and S, which inactivate F5a and F8a
- TFPI released w tissue destruction, inactivating F&a
- Heparin like molecules activated AT3 which inactivates F2a and others
- Endothelium inactivates F2a
Summary of normal hemostasis:
________ plays a pivotal role in initiation and cessation of clotting
initiation of the platelt plug formation and _________ occur simultaneously
______ is the driving force behind platelet activation, fibrin generation, endothelial acitvation and fibrinolysis, and natural anticoagulation activity
Why is this process tightly regulated
- endothelium plays a pivotal role in intiation and cessation of clotting
- initiation of the platelet plug formation and clotting cascade occur simultaneously
- thrombin is the driving force behind platelet activation, fibrin generation, endothelial activation and fibrinolysis and natural anticoagulation activity
- normally this process is tightly regulated to limit clotting to the desired site and prevent widespread inappropriate thrombosis
What are the 4 laboratory screenings for primary hemostasis?
platelet count and morphology
bleeding time
platelet function ( PFA-100, Platelet aggregation studies)
vWillebrand studies (vW antigen, vW activity)
What are 5 laboratory screening test to assess secondary hemostasis?
Activated clotting time (ACT)
Prothrombin time (PT)
Activated partial thromboplastin time (aPTT)
Fibrinogen activity
Thrombin time
What is a platelet count based on? Is it automated or manual?
- based on size as determined by electrical impedance
- automated
What are 2 abnormal findings from a platelet count?
- Thrombocytopenia
- Thrombocytosis
- reactive (inflammation, iron deficiency anemia)
- myeloproliferative neoplasms (CML, ET, PV, PMF)
What is the normal morphology of paltelets? What are 2 abnormal morpholigies and what may cause them?
- Normal:
- variably sized
- smaller than a RBC
- Granulated
- Abnormal
- hypogranular (MDS, Grey platelet syndrome)
- Giant (myeloproliferative neoplasms, bernard soullier disorder, MHY9 disorders)
What does bleeding time test?
in vivo test of vascular integrity, platelet count and function
time when the patient stops bleeding
no longer performed
What is the gold standard platelet function asssay?
platelet aggregation study
- add agonist to platelets (PRP), measure PLT aggregation. Done manually
What are the two purposes for platelet function assays?
- Screening; PFA-100
- for PLT function defects and vW disease
- high sensitivity for severe disease, low for mild, moderate sensitivity to aspirin therapy
- false positives
- Anti-platelet medication monitoring: VerifyNow
- FDA approved for aspirin, clopidogrel responsiveness
There are differences between clotting in vivo and clotting in the laboratory. WHat 3 things are the same across all tests?
clot-based
measure time to form fibrin clot
reported in seconds
How do you measurure Prothrombin time(PT)? What does it test? What are 2 uses? How is it repoerted and how does heparin influence it?
- combine tissue factor, lots of phospholipid, and calcium
- tests the extrinsic and common pathway (F7, F10, F2, F5, fibrinogen)
- uses: Screening for factor deficiencies and warfarin monitoring
- reported in seconds and international normalized ratio (INR)
- not prolonged with heparin
Why do we measure INR?
INR normalizes for variability across labs!
it is not prolonged with heparin
How do you measure activated partial thromboplastin time (aPTT)? What does it test? WHat are 3 uses? how does it respond to warfarin?
- combine activator, low phospholipid, calcium
- tests intrinsic and common pathway (F12, F11, F10, F9, F8, F2, F5, fibrinogen)
- uses: screen for factor deficiencies, lupus anticoagulant, heparin monitoring
- variably sensitive to warfarin
How are mixing studies done?
- can be done with PT or aPTT
- Mix 1 part patient sample with 1 part normal plasma (1:1)
- corrects with factor deficiencies
- fails to correct with inhibitors (drugs, lupus anticoagulation)
What do D dimers asses?
they are a lab for fibrinolysis
measurable breakdown product of plasmin-induced fibrinolysis
imunoassay
How do you measure Thrombin Time (TT)? What are 3 things that could make it abnormal or prolonged?
- add thrombin
- measure time to form fibrin clot
- abnormal/prolonged
- heparin, direct thrombin inhibitors
- A/hypofibrinogenemia
- Dysfibrinogenemia
How do we test fibrinogen activity? WHat would cause a low or high value?
- add thrombin
- measure a thrombin time and compare to a standard curve
- reflects fibrinogen activity and concentration
- reported in mg/dL
- abnormal
- low: a/hypofibrinogenemia
- high: inflammatory state (acute phase reactant)
