The Coagulation Cascade

Elements in Hemostasis

1. Vasoconstriction

2. Formation of stable platelet plug

3. Blood coagulation

What activates platelets?

collagen

Steps of Blood Coagulation (outline)

1. Interaction of blood clotting factors

2. Formation of stable fibrin mesh

3. Entrapment of blood cells

4. Production of red, jelly-like coagulum

Current blood coagualtion theories: Common elements

1. Extrinsic and intrinsic clotting pathways.

2.twelve coagulation factors

3. four discrete stages in coagulation of blood

4. enzymes in blood coagulation

Enzymes

-produced and secreted in an inactive form

-proteolytic in nature-accelerators of biochemical rections

-reaction specific

Serin protease

cleave peptide bonds

Transamidase

forms covalent bonds

Coagulation factors

-most are formed in the liver in precuror forms by vitamin-K dependent process

What does the vitamin-K process do?

-attaches calcium-binding prosthetic groups ont he amino terminal regions of these factors

-introduction of an extra COOH group on the side chain of several glutamic acid residues

-Called gamma-carboxyglutamic acid

Absence of Vitamin K

-Factors 2,7,9,10 are synthesized by are incomplete, lacking the special calcium-binding gamma-carboxyglutamic acids and appear as nonfunctional factors

-known as PIVKA (protein induced by vitamin K absence/antagonism)

What factors are synthesized by the liver?

1,2,5,7,9,10,11,12,12

What factors are not in the liver?

3,4,8

What are the four major stages in blood clotting?

1. Generation of Prothrombin Activator

2. Conversion of Prothrombin to Thrombin

3. Conversion of Fibrinogen to Fibrin

4. Stabilization of Fibrin

Stage I

Extrinsic and intrinsic pathways converge at the final point in stage I where factor X reacts with V to produce prothrombinase

Stage II

Conversion of prothrombin (II) to thrombin by prothrombinase

Stage III

Consists of the catalytic conversion of fibrinogen to fibrin by thrombin (enzyme)

Stage IV

Factor XIII acts to stabilize the unstable fibrin

I

FIBRINOGEN

II

PROTHROMBIN

III

TISSUE THROMBOPLASTIN

IV

CALCIUM IONS

V

PROACCELERIN

VI

ACTIVATED V

VII

PROCONVERTIN

VIII

ANTIHEMOPHILIC factor A

IX

ANTIHEMOPHILIAC factor B

X

THROMBOKINASE

XI

ANTIHEMOPHILIAC factor C

XII

HAGEMAN FACTOR

XIII

FIBRIN STABILIZING FACTOR

How many procoagulants are there?

there are 15

How many procoagulants are cofactors?

two, factors V and VIII

How many plasma glycoproteins are there and what do they do?

There are 6 plasma glycoproteins that serve as anticoagulants.

What are the 8 zymogens?

7,9,10,11,12,13, Pre-Kallikrein, and Prothrombin

(inactive till clotting needed)

What is a serine protease?

-Proteolytic enzymes of the trypsin family.

-Has a reactive seryl amino acid residue in its active -site.

- Acts on substrate by hydrolyzing peptide bonds.

What's considered a serine protease?

IIa, VIIa, IXa, Xa, XIa, XIIa, Kallikrein

2a, 7a, 9a, 10a, 11a, 12a, Kallikrein

What are the 6 cofactors?

5, 8, HMWK, Protein S, Tissue factor "Juice", Thrombomodulin

What do cofactors do?

-Tissue factors (non-circulating constitutive proteins of the subendothelium)

-Each binds a particular serine protease

-when serine proteases are bound they become stabile and have increased reactivity

Describe factor XIII

-XIIIa is a transglutimase

-transfers amino acids among the gamma chains of fibrin polymers

Other plasma procoagulants:

Factor XIII

Fibrinogen

Calcium

vWF (von WIllibrands factor)

Phospholipids

What is vWF?

von Willibrands factor

-large glycoprotein

participates in platelet adhesion

transports VIII

synthesized in megakaryocytes and endothelial cells

What are the 6 anticoagulants? (natural)

Heparin cofactor II

Protein C

Antithrombin

TFPI

Alpha-2-macroglobulin

Alpha-2-antitrypsin

I, Fibrinogen

-glycoprotein

-dimer (consists of three pairs of polypeptide chains, alpha, beta, gamma, linked by disulfide bonds

-CONCENTRATION HIGHEST OF ALL PROCOAGULANTS

-Heat labile, storage stable

-acute phase reactant

-found in platelet granules and is adsorbed on the platelet surface

II, Prothrombin

-single-chain glycoprotein

-vitamin k dependent

-heat and storage stable

-almost entireley consumed in serum

thrombin is activated prothrombin

III, Tissue Thromboplastin

-brain, liver, and placenta have the highest concentration

-complex of phospholipid and protein

-necessary for the activation of VII

-DENATURED BY HEAT

-COFACTOR

IV

Calcium, you need Ca to live! We always have this one...

V, Labile Factor, Proaccelerin

-single-chain glycoprotein

-MOST HEAT LABILE AND IS UNSTABLE IN PLASMA

-activated by thrombin

-COFACTOR (as a cofactor it is bound to prothrombin, enhancing the activation of prothrombin)

VII, Stable Factor, Proconvertin

-Vitamin K dependent

-single-chain glycoprotein

-LOWEST CONCENTRATION IN THE PLASMA

-heat labile, storage stable

-has the shortest half-life

-needs tissue thromboplastin to be activated

-serine protease

(if plasma sits, this one is gone first...most easy leaving)

VIII, Antihemophilic fator

Large multimeric molecule

-HMW (autosomal, endothelium, platelets)

-VWF

-VIII R:Ag

-VII R:Co

Concentrated as cryoprecipitate (cofactor)

-LMW (X-linked) (procoagulant)

-VIII:C

-Cofactor

-------causes coagulation

IX, Christmas Factor

-single-chain glycoprotein

-vitamin K dependent

-Heat labile and storage stabile

-sex-linked inheritance

-activated by XIa or an enzyme from Russell's viper venom

-serine protease

X, Stuart Prower

-two chianed glycoprotein

- vitamin K dpendent (2,7,9,10)

-activated by VIIa and IXa-Ca-Pf3

-activated by enzyme in Russell's viper venom

-activation is the first step in the common pathway

-serine protease

XI, Plasma Thromboplastin Antecedent

-two similar polypeptide chains

-heal labile and CONCENTRATION INCREASES IN STORAGE

-circulates in the plasma with HMWK

-activated by trypsin and XIIa

-serine protease

XII, Hageman Factor

-sngle-chain glycoprotein

-heat labile and storage stable

-activated by negative charged surfaces

-serine protease

What are example of negatively charted surfaces?

glass

ellagic acid

collagen

celite

homocysteine

fatty acids

endotoxins

XIII, Fibrin-stabilizing Factor

-two pairs of nonidentical polypeptide chains

-heat labile and storage stable

-trapped in the fibrin clot as it is activated by thrombin

-XIIIa is essential in forming the covalent bonds between adjacent fibrin monomers

-TRANSGLUTAMINASE

Fletcher Factor

-AKA Prekallikrein

-circulates complexed to HMWK

-Converted to kallikrein by XIIa (12a)

Fitzgerald Factor

-AKA HMWK

-single-chain glycoprotein

-no proteolytic activity-involved in contact activation-circulates complexed with prekallikrein and factor XI

-bradykinin is released when kallikrein acts on HMWK ( inflammatory cascade)

Coagulation mechanisms

Contact activation

-initiated by contact with a negatively charged surface surface

-XII, IX, prekalikrein, HMWK (contact factors)

Intrinsic pathway activation of X

Extrinsic pathway activation of X

Alternate pathways

Contact Activation

-do not require calcium

-readily adsorbed onto negatively charged surfaces

-activates fibrinolysis and the inflammatory systems of kinin and complement

What causes a conformation change during contact activation?

XII is adsorbed onto the surface

What does XIIa do in the presence of HMWK?

activates prekallikrein to generate kallikrein and XI to XIa

What do kallikrein and XIa do together?

activate XII in a feedback system that amplifies the reaction

More contact activation facts:

-autodigestion and kallikrein hydrolysis of XII

-XII fragments activate prekallikrein and plasminogen proactivator (fibrinolytic and kinin systems)

Kallikrein acts on HMWK to produce bradykinin which:

-increases vascular permeability

-contracts smooth muscle

-causes pain

Plasminogen proactivator is a complex of kallikrein and XIIa which:

Concert plasminogen to plasmin (initiates fibrinolysis)

What is the final step of contact activation?

Completes with activation of XI

What does the extrinsic pathway include?

3, 7, 10, 5

What does the intrinsic pathway include?

12, 11, 9, 8, 10, 5

What does thrombin do in the common pathway?

cleaves fibrinogen to produce fibrin monomers (thrombin speeds up the reaction)