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MHD > Hemostasis I and II > Flashcards

Hemostasis I and II Flashcards

1
Q

Normal Hemostasis

A

Process by which ruptured vessels undergo changes to prevent blood loss

Major event: hemostatic plug

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2
Q

Thrombosis

A

Abnormal hemostasis

Process which blood forms a clot within intact blood vessels (have not ruptured)

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3
Q

Abnormal hemostasis

A

Pathologic process that represents activation of clotting system when there are no ruptured vessels

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4
Q

Initial hemostatic response

A

Vasoconstriction, reduce blood loss

Neurogenic mechanisms

Humoral factors released from endothelium (ENDOTHELIN, vascoconstrictor)

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5
Q

Primary hemostasis

A

Platelet adherence

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6
Q

Primary hemostasis

Initial binding

A

GPIb binding to VonWillebrand factor (vWF)

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7
Q

Primary hemostasis

alpha granules

A 
aka light granules
Release PF4 (heparin-binding chemokine), PDGF (platelet derived growth factor), other proteins, fibrinogen, fibronectin, coagulation factors V and VIII, TGFB
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8
Q

Primary hemostasis

beta granules

A 
aka dense (dark) granules
Release ADP, Ca+2, histamine, serotonin, and EPI
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9
Q

Primary hemostasis

Aggregation

A

Release of ADP from dense granules = upregulates GPIIb/IIIa receptor on platelets

TXA2 synthesized by platelet cyclooxygenase (COX) (promotes platelet aggregation)

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10
Q

Secondary hemostasis

A

Release of Tissue Factor by endothelial cells combine with platelet factors to INITIATE plasma coagulation cascade ultimately FORMING THROMBIN (which converts firbinogen to fibrin and cements platelet-thrombin plug)

Coagulation proteins form complexes on platelet surface via phospholipid of the platelet membrane

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11
Q

Role of Endothelium

A

Modulate elements of hemostasis-coagulation sequence

Antithrombotic effect (normal state)
Prothombotic effect (response to injured endothelium)
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12
Q

Anti-thrombotic Effect

Anti-platelet effect

A

Intact endothelium prevents platelets & coag proteins from contacting subendothelial collagen

Normal endothelial cells secrete prostacyclin and NO that prevents aggregation

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13
Q

Anti-thrombotic Effect

Anti-coagulant effect

A

Heparin-like molecules combine with antithrombin to inactivate thrombin and other coagulation factors

Thrombomodulin combins with thrombin to activate protein C

Endothelium also secretes protein S which is cofactor for protein C activation (which inactivate factors V and VIIIa)

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14
Q

Antithrombotic Effect

Fibrinolytic effect

A

Endothelial cells also secrete plasminogen activators (T-PA) which promote fibrinolysis

Plasminogen -> plasmin (dissolves the clot)

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15
Q

Prothombotic Effect

A

Injury causes a loss of endothelial cell platelet/blood clotting inhibition

Endothelial cells secrete vonWillebrand factor (bridges platelets and subendothelial collagen) PLATELET ADHESION

Endothelial cells also secrete tissue factor (activates extrinsic sequence of coagulation cascade). Cytokines released by injured endothelial cells stimulate synthesis of more tissue factor

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16
Q

Tissue factor

A

Promotes generation of thrombin/formation of a clot

Clot traps other cells (erythrocytes and leukocytes)

17
Q

Platelets

A

Discoid, anuclear cells

Membrane contains glycoprotein receptors (for vWF and fibrinogen)

Glycoprotein IIb/IIIa
GlycoproteinIB
Thrombin
Serotonin
ADP
18
Q

Platelet adhesion

A

vWF binds to subendothelial collagen

GPIb binds to vWF

19
Q

Platelet Activation/Secretion

A

GPIIb/IIIa binds fibrinogen to link platelets, activates platelets

Activated platelets release coagulation factors, ADP, Ca, TXA2

Phospholipid complex (site where coagulation factors/Ca activate intrinsic pathway) activated when phospholipids are exposed on platelet surfaces

20
Q

Platelet Aggregation

A

ADP (dense granules) TXA2 (COX) recruit, activate, and aggregate platelets

Serotonin and TXA2 vasoconstrict

Intrinsic pathway activated (via phospholipid complex) and thrombin is formed

Thrombin converts fibrinogen (linking platelets) to fibrin which makes irreversible (secondary) hemostatic plug

21
Q

Coagulation System

A

Network of proenzymes, ultimately forms thrombin

22
Q

Stabilization of fibrin clot

A

When fibrinogen is converted by thrombinIIa to fibrin.

XIIIa (transaminase enzyme) and TAFIa stabilize

23
Q

Intrinsic pathway

A

Activated by subendothelial collagen (SEC), tested via PTT, affected by HEP (heparin). Disfunction leads to hemophilias

XII to XIIa (prokallikrein -> kallikrein, HMWK collagen)

XIIa converts XI to XIa

XIa converts IX to IXa

IIa (thrombin) converts VIII to VIIIa

IXa and VIIIa contribute to X

IIa (thrombin) is the product of the pathway and ALSO an amplification factor!

24
Q

Extrinsic pathway

A

Activated by tissue damage/ tissue thromboplastin (TT) AKA TISSUE FACTOR, tested via PT, affected by warfarin.

Tissue factor converted by VII to tissue factor and VIIa

25
Q

Common pathway

A

X converted to Xa (by IXa/VIIa from intrinsic and TF/VII from extrinsic

V converted to Va by IIa (thrombin)

Xa/Va convert II (prothrombin) to IIa (thrombin)

IIa (thrombin) converts I (fibrinongen) to Ia (fibrin)
Fibrin is further stabilized by transaminase XIIIa (STABILIZING FACTOR)

26
Q

Fibrinogen group

A

Factors I (fibrinogen), V, VIII, and XIII

27
Q

Prothombin group

A

Factors II (prothrombin), VII, IX, and X

Binding of Ca

28
Q

Contact group

A

Factors XI, XII, fletcher factor (prekallikrein), fitzgerald factor (HMWK collagen)

29
Q

Other factors

A

Protein C, Protein S, Fibronectin

30
Q

Inhibitors of Coagulation System

A

Plasma proteins

*Antithrombin III (AT)
Heparin cofactor II (HC II)
*Tissue factor pathway inhibitor (TFPI)
Inhibitors to clotting factors
Lupus anticoagulant and antiphospholipid antibodies
Antibodies to coagulation factors (rare)
31
Q

Antithrombin

A

Plasma inhibitor

Mediates anticoagulant actions of heparin

32
Q

Heparin cofactor II

A

Weak inhibitor of thrombin

33
Q

Tissue factor pathway inhibitor

A

Potent inhibitor of tissue factor

34
Q

Fibrinolytic System

A

Network of enzymes that are responsible for the dissolution of a formed clot

Comprised of proenzymes that when converted to their active form facilitate the digestion of fibrinogen

Plasminogen -> PLASMIN

35
Q

Inhibitors of the fibrinolytic system

A

Plasminogen activator inhibitor (PAI)
alpha2-antiplasmin (binds free plasmin)
alpha2- macroglobulin
Thrombin activatable fibrinolytic inhibitor (TAFI)

36
Q

Hypercoagulable state

A

Inbalance o fthe blood coagulation mechanisms leading to thrombotic transitions

37
Q

Primary (genetic) causes of hypercoagulable state

A

Molecular thrombophilias

Inhibitor deficiency

38
Q

Secondary (acquired) causes of hypercoagulable state

A

High risk: sepsis, cancer, trauma

Low risk: pregnancy, hyperlipidemia, drugs

MHD (34 decks)

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