secondary/tertiary hemostasis

coagulation

formation of an insoluble, cross-linked mesh of fibrin that forms on the surface of a primary platelet plug to stop hemorrhage from the vessel

what is the goal of coagulation?

reinforce platelet plug that would probably not hold depending on size of wound

how is the goal of coagulation accomplished?

goal is accomplished through the formation of a fibrin clot

what is the location of where coagulation is occurring?

occurs on the surface of activated platelets that have already formed a platelet plug

what are requirements for coagulation?

1. Calcium

2. Cells

3. Enzymatic cofactors

4. Phospholipids

5. Non-enzymatic proteins

what pathways are coagulation organized into?

1. intrinsic pathway

2. extrinsic pathway

3. common pathway

intrinsic pathway

All factors required for this pathway are circulating in the blood

extrinsic pathway

The factor that initiates the pathway is outside the blood circulation

common pathway

Results in the formation of fibrin

what activates the intrinsic pathway?

Factor 12 activates intrinsic pathways by activating factor 12A

what leads to the activation of Factor 12?

When the negative charges of exposed collagen fibers contact factor 12, this zymogen becomes activated

zymogen

enzyme circulating in blood that is inactive

what do factors 8 and 10 require for activation?

require cofactors → phospholipids and calcium

what point of protelytic cascade are Factor 8 and Factor 10 of the intrinsic pathway?

Factor 8 to Factor 10 at the end-point of the intrinsic pathway is fundamental for initiation of the common pathway

what activates the extrinsic pathway?

Factor 3 activates the extrinsic pathway by activating Factor 7 when circulating in tissue

where is Factor 3 produced?

Tissue factor (factor 3) not produced in liver, but released as a tissue factor from damaged subendothelial tissue cells

what does activated Factor 7 activate in the extrinsic pathway?

Activated Factor 7 will activate factor 10 → calcium required as Factor 7 is a clotting factor

what Factor is the first step in the common pathway?

Factor 10 is the first step in the common pathway; will activate "Prothrombin Activator Complex"

Prothrombin Activator Complex

Factor 10A to form complex with Factor 5A and phospholipid and calcium; this will act as a proteolytic enzyme to activate further complexes in the common pathway

what do proteolytic enzyme do?

will take amino acids to activate following sequences in common pathway

what factors are activated in common pathway?

1. Thrombin (Factor 2A) activated by proteolytic enzyme complex from Prothrombin (Factor 2)

2. Fibrin (Factor 1A) will be activated from Fibrinogen (Factor 1) through Thrombin

what strengthens Fibrin (factor 1A) in common pathway?

Fibrin (1A) is a weak link between fibrin mesh so we will activate factor 13A to make cross-linked fibrin clot = more strong blood clot

thrombin is an amplification factor so..

can amplify Factors 5,8,9, and 13 to make them more effective

where is Antithrombin 3 (AT-3) produced?

protein produced in liver

what is the function of Antithrombin 3 (AT-3)?

Binds to and inhibits factors 10A and thrombin (Factor 2A) ; remember that thrombin is an amplification factor

List the Physiological Anticoagulant molecules

Antithrombin 3 (AT-3)Heparin (Heparan sulfate)

where is Heparin (Heparan sulfate) produced?

Glycosaminoglycan is produced in the liver, lungs endothelial cells, and circulating white blood cells

what is the function of Herapin?

enhances activity of AT-3

why can herapin not be given orally?

large size and charge do not make it absorbed by gut so give parental, infusions, or SQ

what newer anticoagulants are being used?

enoxaparin or oral anticoagulants like rivaroxaban are now in use

what is the role of vitamin K in hepatocytes?

Assist in the carboxylation of coagulation factors, which facilitates the binding of coagulation factor complexes to calcium to activate coagulation factors

what is carboxylation necessary for?

Carboxylation necessary for coagulation factors to be able to bind to calcium to be activated and do their job

describe the process of carboxylation

Vitamin K is reduced ( Vitamin K reductase) and co-factors with Vitamin K carboxylase to carboxylate coagulation factors

what is the source of vitamin K?

gut bacteria

which Factors depend on vitamin K for these coagulation factors to be synthesized in the liver?

Factors 2, 7, 9, and 10

what factors are not produced in the liver?

Factor 3, phospholipids, and Factor 4

Factor 3

synthesized in subendothelial tissue and does not need to be activated

Factor 4

NOT an enzyme, another name for cofactor (calcium)

phospholipids are provided by

platelets

most coagulation factors are synthesized in

the liver and must be activated before they can exert their function

what factors are effected by warfarin?

• Effect extrinsic (factor 7)

• intrinsic (factor 9)

• common (factor 2 and 10) pathway

how does warfarin inhibit the action of vitamin K?

1. Inhibits carboxylation of specific amino acids residues in the clotting factors

2. Inhibits enzyme Vitamin K epoxide reductase

what is the primary physiological effect of warfarin poisoining?

significant reduction in blood coagulation → prolonged bleeding times and risk of hemorrhage

fibrinolysis

a complex process that involves the activation of proteolytic enzymes which aims to degrade the fibrin clot formed at the end of coagulation → restore blood flow!

what must be removed before healing of endothelium can take place?

removal of blood clot

how long does healing of endothelium take?

about 5 days

In a blood clot, endothelium below must be repaired so…

fibroblasts and endothelial cells use mesh fibrin as scaffolding to migrate to wounded tissue and will proliferate, migrate, and recover

what stimulates fibroblasts during fibrinolysis?

platelet derived vascular endothelial growth factors (VEGF)

what stimulates stimulate endothelial cells at the edges of injury to proliferate and migrate to damaged area in fibrinolysis?

EGF, fibroblast growth factor (FGF) and other angiogenic factors

what are the steps of fibrinolysis?

1. Endothelium slowly releases tissue-Plasminogen Activator (tPA)

2. tPA activates hepatic plasma factor plasminogen to plasmin

3. Plasmin is a proteolytic enzyme that hydrolyses fibrin fibers to fibrin degradation products (FDP)

4. FDPs are removed by macrophages; plasmin acts as scissors to cut the links between fibrin

list the Inhibitors of fibrinolytic system

1. Plasminogen Activator Inhibitor-1 (PAI-1)

2. Plasmin inhibitors (Alpha-2-Antiplasmin)

what is Plasminogen Activator Inhibitor-1 (PAI-1)?

Glycoprotein produced by endothelial cells

what influences the production of Plasminogen Activator Inhibitor-1 (PAI-1)?

inflammatory cytokines and endotoxins

what is the function of Plasminogen Activator Inhibitor-1 (PAI-1)?

Interacts directly with tPA and deforms its active sites → prevent the formation of plasmin and fibrinolysis

what is Plasmin inhibitors (Alpha-2-Antiplasmin)?

Alpha-2-antiplasmin is a serine protease inhibitor produced by the liver

what is function of Alpha-2-antiplasmin?

Crosslinked to the active sites of plasmin, irreversibly inhibiting its activity → plasmin will not be active

list the anti-fibrinolytic drugs (lysine derivatives)

1. tranexamic acid

2. epsilon aminocaproic acid

what happens in some greyhounds when we use anti-fibrinolytic drugs?

plasminogen and t-Pa have lysine bound to their receptors so neither can bind to fibrin and clot, this stops exaggerated fibrinolysis

what is happening in a normal dog with fibrin and lysine?

• fibrin binds to blood clot (plasminogen and t-PA) via lysine

• t-PA binding on surface of fibrin will chop plasminogen into plasmin to act on fibrin

in dogs experiencing hyperfibrinolysis, what is the significance of elevated FDPs?

indicate presence of ongoing fibrinolysis

what is common to see in postoperative bleeding ("greyhound bleeders") after surgery?

2. delayed bleeding after the surgery

3. hemorrhagic discharge from the surgical wound

4. skin bruising

how can an increased amount of PAI-1 contribute to a pathogenic thrombotic process?

risk of thrombosis increases

what enzyme will change a fibrin mesh having no cross links to having a crosslinked fibrin mesh?

Factor 13

what will breakdown crosslinked fibrin mesh into D-dimer and other FDPs?

plasmin

what coagulation factor will be first affected when warfarin intoxication has happened and why?

Factor 7, has shortest half-life so will be first to disappear

intoxication with warfarin is associated with which hemostasis?

secondary

von wilhem intoxication is associated with which hemostasis?

primary

what role does factor 3 play in the extrinsic pathway of hemostasis?

it bonds factor 7 to initiate coagulation

what coagulation pathway does factor 3, known as tissue factor, belong to?

extrinsic pathway

what does Factor 10 activate?

factor 8

what is the role of the PAC in the coagulation process?

it converts prothrombin into thrombin

if calcium is removed from a blood sample, how will it affect the coagulation process?

prevents sample from coagulating

what common characteristic is shared by the extrinsic and intrinsic pathway?

both pathways ultimately lead to the activation of factor 10

what is the half-life of fibrinogen?

72-120 hours

what is the half-life of prothrombin (Factor 2)?

72 hours

what is the half-life of proconvertin (factor 7)?

3-6 hours

what is the half-life of factor 8?

12 hours

what is the half life of factor 9?

24 hours

what is the half-life of factor 10?

40 hours

what occurs during the final stage of blood clotting?

formation of a stable fibrin mesh

what is the final stage of blood clotting?

common pathway

what series of events are essential for the coagulation cascade to occur?

enzymatic reactions that transform fibrinogen into fibrin