Blood Coagulation Flashcards
(30 cards)
What process causes the release of factors needed for coagulation?
Platelet agglutination
The extrinsic pathway is a one-step process that activates which key enzyme?
Factor Xa
Which clotting factors directly activate factor X to Xa?
Intrinsically: VIIIa and IXa
Extrinsically: IIIa and VIIa
Which clotting factors convert prothrombin to thrombin?
Xa and Va
What test is used to measure the efficiency of intrinsic blood coagulation?
Activated Partial Thromboplastin Test (APTT)
What is the average range for an APTT ?
30-50 seconds
Prolongations in the aPTT are observed in deficiencies of which factors?
XI, IX, VIII, X, V, prothrombin, or fibrinogen
What test is used for common congenital hemophilias and what deficiencies cause these?
APTT
A-VIII
B-XI
C-XI
What test is used to measure the efficiency of extrinsic blood coagulation?
Prothrombin time (PT)
What coagulation factor is added to a plasma sample in order to test clotting time in a PT test?
Tissue Factor (IIIa)
What is the normal time range for a PT test?
10-15 seconds
Which deficiencies can be detected via a PT test?
VII, X, V, prothrombin, or fibrinogen
Which coagulation test may be used to diagnose acquired bleeding disorders resulting from vitamin K deficiency, oral anticoagulants (e.g. warfarin), and liver disease?
Prothrombin time
True or False: Deficiencies in all of the factors lead to a bleeding tendency in the affected individual.
False: all but factor XII
Prothrombin is activated by two proteolytic cleavages on the carboxyl side of which amino acid residues;
Arg-284 and Arg-320
Binding of Ca2+ to what type of thrombin residue facilitates binding of prothrombin to membrane surfaces and to the prothrombinase complex (FXa:FVa) at the site of injury?
y-carboxyglutamate (Gla) residues
Thrombin causes what substances to be released from platelets at the site of injury within a blood vessel?
ADP, thromboxane A2 serotonin, vWF, phospholipids, seretonin, Factor IV (heparin binding protein)
Name 3 reasons intact normal vascular endothelium does not bind platelets.
(1) receptors and other elements are not exposed
(2) activators such as ADP are rapidly degraded or are not present in blood in sufficient concentration to be effective (3) the endothelium secretes prostacyclin (an inhibitor of platelet aggregation).
What cofactors are required for the post-translational, y-carboxylation of several clotting proteins and their release from the liver?
The reduced form of Vitamin K (KH2)
Ca2+
Which coagulation proteins/glycoprotein cofactor(s) possess an epidermal growth factor domain? Which of these lacks a serine protease?
Factors VII, IX, X and proteins C, Z, and S
Factor S lacks serine protease
Which factors possess a y-carboxyglutamate (Gla) resiude?
II, VII, IX, X, and protein C
Why are newborns given vit K injections soon after birth?
Vit K levels drop due to the sterility of a newborn gut.
Vit K is needed for y-carboxylation and release of clotting factors from the liver
Which factor activates FXIII and what is the function of FXIII?
Thrombin;
FXIII = transglutamidase - forms crosslinks between fibrin soft clots to form hard clots
What are the steps leading to lysis of fibrin clot?
Tissue plasminogen activator (TPA) activates plasminogen to plasmin. Plasmin has a high affinity for fibrin clots and hydrolyzes the clot.
