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Equine Internal Medicine Q&A 03 (view source)
Revision as of 17:35, 5 June 2011
, 17:35, 5 June 2011no edit summary
|q1=What does the prothrombin time (PT) test?
|q1=What does the prothrombin time (PT) test?
|a1=PT tests the extrinsic arm of the coagulation cascade, which begins with activation of factor VII.
|a1=PT tests the extrinsic arm of the coagulation cascade, which begins with activation of factor VII.
|l1=
|l1=Coagulation Tests#Prothrombin Time
|q2=What does the activated partial thromboplastin time (APTT) test?
|q2=What does the activated partial thromboplastin time (APTT) test?
|a2=APTT tests the intrinsic arm of the coagulation cascade, which begins with activation of factor XII.
|a2=APTT tests the intrinsic arm of the coagulation cascade, which begins with activation of factor XII.
|l2=
|l2=Coagulation Tests#Activated Partial Thromboplastin Time
|q3=Which clotting time, PT or APTT, would you expect to be prolonged first in a horse with hepatic failure, and why?
|q3=Which clotting time, PT or APTT, would you expect to be prolonged first in a horse with hepatic failure, and why?
|a3=The PT, because factor VII has a very short half-life. Therefore, with decreased production, the available factor VII is depleted more quickly than the factors with longer half-lives.
|a3=The PT, because factor VII has a very short half-life. Therefore, with decreased production, the available factor VII is depleted more quickly than the factors with longer half-lives.
|l3=
|l3=Liver Failure
|q4=Horses with liver failure are often endotoxaemic due to the failure of the hepatic macrophages to phagocytoze gut-derived endotoxin. Can you explain why this endotoxaemia might exacerbate factor VII consumption?
|q4=Horses with liver failure are often endotoxaemic due to the failure of the hepatic macrophages to phagocytoze gut-derived endotoxin. Can you explain why this endotoxaemia might exacerbate factor VII consumption?
|a4=Endotoxin stimulates extrinsic coagulation by stimulating the expression of tissue factor on the surface of mononuclear cells. Tissue factor binds factor VII, thereby initiating the extrinsic coagulation cascade.
|a4=Endotoxin stimulates extrinsic coagulation by stimulating the expression of tissue factor on the surface of mononuclear cells. Tissue factor binds factor VII, thereby initiating the extrinsic coagulation cascade.
|l4=
|l4=Coagulation Tests#Introduction
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