Coagulation Flashcards
(23 cards)
Steps in stopping bleeding
Blood Coagulation Release of Tissue Factor at injury site Activation of coagulation cascade Formation of thrombin • Converts fibrinogen to fibrin • Stimulates further platelet recruitment and release • Permanent plug produced
First three general steps of the coagulation cascade
Vasoconstriction ( caused by endothelin release)
Primary hemostasis
Secondary hemostasis
What are Platelets
-Small anucleate cells
-Derived from the cytoplasm of
megakaryocytes
-Membrane glycoproteins participate in
adhesion and aggregation
-Release secretory granules
-Essential for primary hemostasis
What is in alpha granules (platelets)
Fibrinogen, fibronectin, factors V and VIII,
platelet factor 4, growth factors (PDGF,
TGF-b
What is in dense granules of platelets
ADP, ATP, ionized calcium, histamine,
serotonin, and epinephrine
Three Important Reactions that platelets are involved in
- Platelet Adhesion and shape change
- Platelet Secretion (release reaction of
granules) - Platelet Aggregation
How is a platelet plug formed
• Platelet Aggregation -ADP (potent mediator) -Thromboxane A2 (vasoconstrictor) -Thrombin (seal platelet plug) • Fibrinogen -Binds adjacent platelets and enhances aggregation -GPIIB-IIIa receptor needed for binding
What receptors on the platelet bind to receptors on the endothelium?
GpIb on the platelet binds to Von willebrand factor on the subendothelium . GpIIb-IIIa binds to fibrinogen which connects one platelet to another. Deficiency of GpIb - Bernard - soulier, Von willebrand factor - Von willebrand disease
Which factors are dependent on vitamin k ?
Factors II, VII, IX, X,
Protein C and Protein S
What activates the intrinsic pathway? What happens next?
–Activated in vitro by contact activation XII–Activated factor XII links coagulation, fibrinolytic, kinin and complement system–converts XI to XIa which Converts IX to IXa
What activates the extrinsic pathway? What gets converted in this pathway?
–Activated by tissue factor
– tissue factor converts VII to VIIa which goes on to convert IX to IXa or X to Xa
What activates the common pathway? What factors are involved with it?
Activation of Factor X by the intrinsic system, extrinsic system or both
X ➡Xa converted by VIIa (ex) or IXa (in)
II(prothrombin) ➡ IIa (thrombin) converted by Xa +Va
Fibrogen ➡ fibrin converted by thrombin ( IIa)
Role of Thrombin (Factor II) ( 6)
- Key Factor in extrinsic and intrinsic system
- Converts fibrinogen to fibrin
- Activates factor XIII
- Enhances factor V and VIII activity
- Induces platelet aggregation
- Stimulates endothelium to produce PGI2 for vessel relaxation
What is the final step in the repair of a blood vesssel
Fibrinolysis
What are the Plasminogen Activators and Inhibitors of the Plasminogen-plasma system
Activators –Tissue plasminogen activator (t-PA) –Urokinase plasminogen activator (u-PA) –Streptokinase Inhibitors -a-2 antiplasmin -antithrombin III
Prothrombin Time Test (PT)
–Measures how effectively factor VIIaalong with tissue factor (III) activates factor X –Extrinsic Pathway –Performed by adding tissue thromboplastin (tissue factor) to patient plasma
What causes an Abnormal PT
Think-Extrinsic or Common Pathway Deficiency –Decreased Factor VII –Mildly decreased Factor II, V, X –Warfarin (at initiation) –Mild DIC –Mild Vitamin K Deficiency (II, V, IX, X)–Mild liver disease
What does Activated Partial Thromboplastin
Time-aPTT test?
–Measures activation of factor XII which
activates Prekallikrein (Fletcher factor) andHMWK (Fitzgerald factor)
–Kallikrein feeds backs to factor XIIa to
speed up the intrinsic reaction
–Performed by adding partial
thromboplastin, particle activators and
calcium to patient plasm
What would cause an Abnormal PTT
Think-Intrinsic or Common Pathway Deficiency –Heparin –Decreased factor VIII, IX, XI –Factor Inhibitor –“Lupus” inhibitor –Decreased factor XII, prekallikrein, HMW kininogen
What would cause a Prolonged PTT and PT?
Decreased Factor II, V, X, fibrinogenWarfarin Rx (therapeutic) Heparin (Very high doses) DIC Vitamin K Deficiency Liver disease Therapeutic Fibrinolysis
What is Thrombin Time and what would cause an abnormal one?
Direct measure of the ability of thrombin to clot fibrinogen Abnormal TT –Heparin –Decreased or abnormal Fibrinogen –DIC –Therapeutic fibrinolysis –Liver Disease –Paraproteins
If No Abnormalities are on Screening Tests what Causes of Bleeding should be considered ?
- Von Willebrand’s disease
- Factor XIII deficiency
- Mild coagulation defects
- a-2 antiplasmin deficiency
If there is a Prolonged Bleeding Time and normal PT,PTT and platelet count what is to be considered? What about a prolonged bleeding time and decreased platelet count? What about a prolonged bleeding time and abnormal PTT?
Prolonged Bleeding Time
–Normal platelet count, PT and PTT
Drugs (ASA), Vascular or Platelet
Function Disorder, or von Willebrand’s disease
–Decreased Platelets
Thrombocytopenia, Drugs or platelet
defect
–Abnormal PTT
Von Willebrand’s disease
–Not a predictor of surgical bleeding
