Blood: 4.2: 2a hemostasis Flashcards
What does thrombin do?
it converts fibrinogen to fibrin
What is the ristocetin test?
- ristocetin + platelets –> aggregation
- if there’s no vWF, they won’t clump
In 1a hemostasis, the primary problem is ______.
superficial bleeding
What test would check the effect of liver failure on coagulation?
PT
______ and _______ are the major clinical feature of 2a hemostasis.
- Deep bleeding (into muscles and joints)
- rebleeding after surgery
What is the PTT test?
- a measure of intrinsic and common pathways
- PTT = more letters than PT, so it’s the LONGER pathway
- 12, 11, 9, 8, 10, 5, 2, 1
What is the most common subtype of vWF disease? What is the result?
- auto. dominant
- decreased vWF levels
What is Vitamin K deficiency?
disrupted coagulation
What does low vWF cause?
impaired platelet adhesion
Why is Vitamin K so important for coagulation?
it’s necessary for gamma-carboxylation of factors 2, 7, 9, 10, C, and S
Platelet activation requires calcium. Where does the calcium come from?
dense platelet granules
How does desmopressin work?
- it increases vWF release from the Weibel-Palade bodies in endothelial cells
- * W for vWF, P for P-selectin
The clinical severity of hemophilia A depends on _____.
the degree of deficiency
Where does Vitamin K come from?
normal gut flora
Platelets adhere using vWF and _____.
GPIb
How do hemophilia A pts present?
- deep tissue, joint, and post-surg bleeding
- these are classic s/s of a secondary hemostasis disorder
Hemophilia A lab results?
- increased PTT
- normal PT
- decreased FVIII
- normal platelets
- normal bleeding time
Which factor is most commonly targeted by coagulation factor inhibitors?
factor VIII (8)
What gets cross-linked to generate a stable platelet plug?
fibrin
Why does long term Abx therapy cause Vitamin K deficiencies?
- vit K is synthesized by normal gut flora
- loss of gut bacteria = loss of vitK
What is the treatment for Hemophilia A?
- give recombinant factor VIII
What is another name for Hemophilia B?
Christmas disease
What molecule links the platelets via GPIIb/IIIa?
fibrinogen
What happens when large volume transfusions are given?
coagulation factors are diluted, leading to deficiencies
What is the PT test?
- a measure of extrinsic and common pathways
- PT is SHORTER than PTT, so PT is less factors
- factor 7, 10, 5, 2, 1
Where are the coag. cascade factors produced?
in the liver
_____ blocks epoxide reductase.
Warfarin/Coumadin
What is hemophilia A?
- an X-linked recessive defect of factor VIII (8)
- can be de-novo mutation
- * hemophilia AAAAA-eight
In which pts can vitamin K deficiency present?
- newborns
- long-term Abx users
- malabsorption (bc it’s a fat soluble vitamin)
- liver failure (less production of factors and they’re not activated bc of loss of epoxide reductase)
What is the goal of 2a hemostasis?
to stabilize the weak platelet plug
What are the lab findings in vWF disease?
- increased bleeding time
- increased PTT (bc vWF stabilizes factor VIII)
- normal PT
- abnormal ristocetin test
What activates factor 12 (the intrinsic pathway)?
- subendothelial collagen (SEC)
- * PTT and SEC are both 3 letters
What is Hemophilia B?
- a genetic factor IX (9) deficiency
- resembles hemophilia A
What is the order of the common pathway, starting at 10?
- 10, 5, 2, 1
- “1 x 2 x 5 = 10”
What is a coagulation factor inhibitor? Which is most common?
- an acquired autoantibody against a coagulation factor, impairing its function
- anti-FVIII (factor 8) most common
What is the receptor for platelet aggregation?
GPIIb/IIIa
Which test is better for measuring warfarin/Coumadin?
- PT/INR
What 3 things does activation require?
- exposure to an activating surface
- phospholipid surface
- calcium
The goal of the coag. cascade is to produce factor ____.
X
“produce a perfect 10”
Why is the PTT increased in vWF Disease?
vWF stabilizes factor VIII (8)
Vitamin K is activated by ____ in the ____.
- epoxide reductase
- liver
Activation requires a phospholipid surface. Where does this come from?
the surface of the platelets
How does a pt with vWF disease present?
mild mucosal and skin bleeding
Clinically, how can you tell the difference btw Hemophilia A and a coagulation factor inhibitor against factor VIII?
A mixing study: the increased PTT can be corrected in Hemophilia A by mixing pt’s plasma with a normal plasma, but this can’t happen if an inhibitor is present
What is the order of the intrinsic pathway factors, ending at 10?
12 –> 11 –> 9 –> 8 –> 10
In general, a disorder of 2a hemostasis is due to _____.
factor abnormalities
How does 2a hemostasis achieve its end goal?
via the coagulation cascade
What is Von Willebrand disease?
- a deficiency of vWF
- the most common inherited coagulation disorder
What activates factor 7 (the extrinsic pathway)?
- tissue thromboplastin (TT)
- * TT and PT are both 2 letters
What is the order of the intrinsic pathway factors, ending at 10?
7, 10
How is vitamin K deficiency prevented in newborns?
they’re all given a prophylactic vitamin K shot at birth
What is the end product of the coagulation cascade?
thrombin
Which test is better for measuring heparin?
- PTT
- * PTT and HEP are both 3 letters
What is the tx for vW Disease ?
desmopressin
