Blood Coagulation- Test 1

Front 1

ATIII-Heparin inhibits which elements of the coagulation cascade?

Back 1

Active serine proteases IXa, Xa, XIa, XIIa, VIIa.

ie, ATIII is a SERPIN
Low levels of active ATIII are maintained to prevent unnecessary clots.

Front 2

Warfarin inhibits which elements of coagulation cascade?

How does it work?

Back 2

Inhibits ZYMOGEN form of serine proteases:

II (Prothrombin), VII, IX, X,

It inhibits the Vitamin K dependent gamma-carboxylation of these serine proteases. Without gamma-carboxyl groups, they can't bind Ca+2 and are inactive.

Front 3

What are the non-enzyme cofactors?

Which enzymes require them?

Back 3

VIIIa- required by IXa

Tissue factor- required by VIIa

Va- required by Xa

Front 4

ATII-Heparin

Back 4

Irreversibly inhibits ALL serine proteases in cascade.

Front 5

What is required for the cross-linking of Fibrin (Ia)?

Back 5

XIIIa- this is not a protease, but rather a transglutaminase.

Cross-links Gln and Lys side chains in fibrin to create a clot.

Front 6

Steps in Intrinsic Pathway

Back 6

Damaged surface

Kininogen and Kallikrein induce XII--> XIIa

XIIa induces XI-->XIa

XIa induces IX-->IXa

IXa + VIIIa induces X-->Xa

Xa + Va induces Prothrombin (II) --> Thrombin (IIa)

IIa induces Fibrinogen (I)--> Fibrin (Ia)

Fibrin Ia + XIIIa (transglu-ase) forms blood clots

Front 7

Steps in Extrinsic Pathway

Back 7

Trauma

VII-->VIIa

VIIa + TF induces X-->Xa

Xa + Va induces Fibrinogen (I)--> Fibrin (Ia)

Ia + XIIIa (transglu-ase) forms blood clots

Front 8

What makes up a clot

Back 8

Fibrin (starts out as loose strings, then forms solid mesh via cross-links)

Trapped platelets & RBCs

All this forms a scab

Front 9

What measures Extrinsic Pathway?

What is main inhibitor of EP?

Back 9

Prothrombin Time (PT)

Warfarin is main inhibitor

Front 10

What measures Intrinsic Pathway?

Main inhibitor of IP?

Back 10

Activated thromboplastin time (aPTT)

Heparin is main inhibitor

Front 11

PT and aPTT in relation to platelet function

Back 11

These measurements use plasma rather than whole blood, so they don't measure platelet function

Front 12

Platelet count

Back 12

Should be above 50,000 per mm3

Front 13

What inhibits platelet function?

Back 13

Aspirin- irreversibly inhibits COX1 and COX2

Ibuprofen- Reversibly inhibits COX1 and COX2

Front 14

How are platelets formed?

How long before having surgery should you stop taking Aspirin?

Back 14

Platelets form by budding off megakaryocytes, so lack a nucleus and cannot replace dead COX1 (as caused by Aspirin).

Half-life of platelets is 10 days, so need to stop taking Aspirin 10 days before surgery so new platelets can form that have functional COX1

Front 15

Vitamin K

Back 15

Needed for gamma-carboxylation of SERPINS II, VII, IX, and X to form gamma-carboxyglutamic acid residues (Gla)

Gla allows clotting factors to bind Ca+2, which anchors them to phospholipid membranes (to phosphatidyl serine) of the platelets at the injury site

Front 16

Phosphatidylserine

Back 16

Normally on cytoplasmic side of lipid bilayers, but is on outside of activated platelets.

Gla residues w/Ca+2 bind to phosphatidylserine so the clotting factors are anchored to the platelets.

Front 17

How does Warfarin (Coumadin) work?

Back 17

It inhibits the enzyme that reduces Vit K

Reduced Vit K is necessary for gamma-carboxyglutamation.

Thus Ca+2 can't bind and the cofactors can't be anchored to phophatidylserines on platelets.

Front 18

Warfarin metabolism

Back 18

Metabolized by cytochrome p450 system.

But at different rates in different people-->due to genetics. Can understand with pharmacogenomics.

Warfarin contains a racemic mixture of R and S forms.

S accts for 60-70% of anti-coag respone.

R accts for 30-40% of response.

Different p450s metabolize these at different rates, and since there are numerous p450 variations (~26), need to know which ones a person has.

Front 19

Cytochrome p450 variations

Back 19

Very slow p450: 1/2 normal Vmax, 1/2 normal Kcat

Slow p450: 10x normal Km

Front 20

Heparin

Where in cells?
How is it isolated?

Back 20

Drug used to control clotting.

Found in granules of mast cells.

Isolated from intestinal mucosa of pigs.

Front 21

Contaminated Heparin

Back 21

Contained Over Sulfated Chondroitin Sulfate (OSCS), which made Heparin appear to be very active for clotting inhibition, but in patients activated the complement cascade, producing anaphylactic responses & killing patients.

Front 22

How does Heparin work?

Back 22

Activates ATIII, a SERPIN that acts on proteases IX, X, XI, XII, and VII.

Heparin-like molecules on vessel endothelial cells activate ATIII and keep uncontrolled clotting from occuring. Heparin is also contained in mast cells, but it is bound tightly to serine proteases there and doesn't seem to have impact on clotting.

Front 23

How does ATIII work?

Back 23

Has Arg in its inhibitor site. When heparin binds, conformation change occurs that allows it to react with Thrombin, etc in the cascade.

Front 24

A1-AT Pittsburgh

Back 24

Normal A1-AT acts on elastase, it does not require heparin for activation.

A1-AT Pitt has a Met-->Arg, so it works on thrombin instead of elastase, but still does not require heparin. Ie, its always active and prevents clotting--> Hemophilia.

Front 25

Factor VIII deficiency

Back 25

Leads to hemophilia.
X-linked Recessive.
Anti-hemophilic factor

Front 26

vWF

Back 26

Glycoprotein that helps platelets to clump & stick to vessel wall by binding to proteins on platelets & collagen.

Also, carries VIII in the blood. VIII degrades quickly when not attached to vWF.

Front 27

vWF

Back 27

Glycoprotein that helps platelets to clump & stick to vessel wall by binding to proteins on platelets & collagen.

Also, carries VIII in the blood. VIII degrades quickly when not attached to vWF.

Front 28

vWD

Back 28

Deficiency results in poor platelet clumping & reduced VIII, so ineffective clotting.

Affects 1% of pop, men & women.

Front 29

Cryoprecipitate

Back 29

Thawing of frozen blood plasma
Contains fibrinogen, vWF, FVIII, FXIII, and fibronectin.

Used to treat vWF and FVIII deficiency.

Does not contain FIX, so can't be used for that type of hemophilia.

Front 30

Protein C

Back 30

slows coagulation by degrading Factors Va and VIIIa.

Activated because when enough thrombin has been produced to form fibrin, the excess thrombin binds to thrombomodulin on endothelial cells.

Front 31

Ways endothelial cells favor thrombosis:

Back 31

Damage to wall exposes tissue factor, inducing extrinsic pathway.

Damage exposes collagen; vWF binds to collagen and to platelets to hold them in place.

Fibrin holds platelet clot to damaged site on vessel

Front 32

Ways endothelial cells inhibit thrombosis:

Back 32

Heparin-like molecules on ECs activate ATIII

TF inhibitors on ECs inactivates VIIa

Thrombin bound to thrombomodulin on EC activates Protein C, degrading Va and VIIIa.

ECs make PG12 and NO to inhibit platelet aggregating.

ECs make tissue plasminogen activator-->degrades fibrin.

Front 33

Fibrinogen

Back 33

Large, hexameric
2 each of alpha, beta, gamma chains
Made by hepatocytes
Cleaved by thrombin to produce fibrin

Front 34

Fibrin

Back 34

Made when thrombin cleaves fibrinopeptides A and B from fibrinogen.

Removal of fibrinopeptides allows ionic bonds to form between fibrin strands.

Goes from soluble fibrinogen to insoluble fibrin.

Front 35

XIIIa

Back 35

Transglutaminase-

Forms crosslinks between Gln and Lys in Fibrin

Front 36

Plasminogen

Back 36

A zymogen of plasmin, which degrades fibrin.

Activated by tissue plasminogen activator (tPA).

Front 37

tPA

Back 37

tissue plasminogen activator. Yields active plasmin from plasminogen.

Can be injected into blood stream to treat clots clinically.