Download Roles of Vessel Endothelial Cells in Physiological

Haemostasis
dr Sri Lestari Sulistyo Rini, MSc
Five Stages of Hemostasis
1. Vessel spasm
2. Formation of the platelet plug
3. Blood coagulation or development of
an insoluble fibrin clot
4. Clot retraction
5. Clot dissolution
The Vascular Phase
• A cut triggers
vascular spasm
• 30-minute
contraction
Figure 19–11a
3 Steps of the Vascular Phase
1. Endothelial cells contract:
– expose basal lamina to bloodstream
2. Endothelial cells release:
– chemical factors: ADP, tissue factor, prostacyclin
– local hormones: endothelins
– stimulate smooth muscle contraction and cell
division
3. Endothelial cell membranes become “sticky”:
– seal off blood flow
Functions of Thrombin
• Stimulates formation of tissue factor
– stimulates release of PF-3:
– forms positive feedback loop (intrinsic and
extrinsic):
• accelerates clotting
The Platelet Phase
• Begins
within
15
seconds
after
injury
Figure 19–11b
Platelets
•
•
•
•
Small fragments of megakaryocytes
Formation is regulated by thrombopoietin
Blue-staining outer region, purple granules
Granules contain serotonin, Ca2+, enzymes,
ADP, and platelet-derived growth factor
(PDGF)
Roles of Vessel Endothelial Cells in
Physiological Hemostasis
Roles are close related to its endocrine functions
① Vessel endothelium serves as barrier
between underendothelial structure (namely,
collagen) and blood. As soon as collagen
expose to blood, hemostasis of platelet is
immediately activated to form thrombus
blocking wounded vessels.
② Platelet activation can releases constrictive
factors (TXA2, ET-1, 5-HT, etc) making vessel
convulsion, lasting about 60 sec.
③ Stimulated vessel endothelial cells release
coagulative factors and Promoting
coagulative material to realize, speed up
blood coagulation. At the same time, cells
also release anticoagulative factors and
fibrinolysis material to modify blood
coagulation.
Endocrine functions of vessel
endothelial cells
① Material related to hemostasis are basal membrane,
collagen (III, IV), microfibril, elastin, laminin,
ectonectin, fibronectin, von Willebrand factor (vWF),
protein enzyme, protein enzyme inhibitor, adhesive
amylose, etc.
② Anticoagulative material: They are prostacyclin
(PGI2), endothelium-derived relaxing factor (EDRF or
nitric oxide, NO), tissue-type plasminogen activator
(tPA), uPA, ADPase, ATIII, heparin sulfate, protein C,
thrombomomodulin (TM), plasminogen activator
(PA).
Endocrine functions of vessel
endothelial cells
③ Promoting coagulative material: Tissue factor,
vWF, blood clotting factor V, plasminogen
activator inhibitor (PAI-1, PAI-2, ATIII), TNFα,
interleukin-1 (IL-1).
④ Vessel constricting and relaxing modulators:
endothelin-1 (ET-1), EDRF (NO), PGI2, etc.
Platelet
• Normal value: 100×109 ~ 300×109, range
from 6%~10%
• Normal changes: more number in the
afternoon than in the morning, more in
winter than in spring, more in the venous
blood than capillary, after sport↑,
pregnacy↑.
Life- Span and Breakage of Platelet
• Life-span: Averagely, 7~14 days in the blood. It
can be consumed when it displays
physiological functions.
• Breakage: Aged platelet can be processed by
phagocytosis in liver, spleen and lymphatic
node.
Function of Platelet
• Functions:
1. It maintains capillary endothelial cells
smooth and integrated (repairing endothelium
and providing nutrition).
2. It is involved in physiological hemostasis.
• Platelet and clinic relation:
decrease of platelet, abnormal immune
reaction, will results in hemorrhage or
bleeding, purpuric symptom.
Platelets
• Form a temporary platelet plug that
helps seal breaks in blood vessels
• Circulating platelets are kept inactive and
mobile by NO and prostacyclin from
endothelial cells of blood vessels
Physiological Characteristics of Platelet
• Thrombocyte adhesion: its membrane
glycoprotein (GP, GPIb/IX and GPIIa/IIIb),
collagen (underendothelial structure), vWF
(plasma component), fibrinogen are involved in
adhesion.
Mechanism: Exposed collagen + vWF → vWF
changes → platelet membrane glycoprotein +
changed vWF → Thrombocyte adhesion.
• Thrombocyte aggregation:
induced by physiological factors such as
ADP, thromboxane A2 (TXA2), epinephrine,
5-HT, histamine, collagen, thrombin,
prostacyclin,etc and by pathological
factors like bacteria, virus, immune
complex, drugs, etc.
The process can be separated into two phases:
phase one is reversible aggregation and phase
two irreversible aggregation. Two phases
require Ca2+, fibrinogen and energy
consumption
• Mechanism : Various factors+corresponding
receptors on the platelet →changes in the
second messenger within platelet →cAMP↓,
Ip3↑, Ca2+↑, cGMP↑→ platelet aggregation.
• Thrombocyte release:
ADP, ATP, 5-HT, Ca2+ released from dense
body, and β-platelet globin, PF4, vWF,
fibrinogen, PFV, PDGF, thrombin sensitive
protein from α-granule, and acid protein
hydrolyzed enzyme, tissue hydrolyzed
enzyme from lysosome.
• Thrombocyte contraction:
Loose platelet thrombus could turn into
compact platelet thrombus by Ca2+ release
and cytoskeleton movement
(filament/canaliculus) within platelet.
Inactive Platelet
Under the electronic microscope
Activated Platelet for Hemostasis
Under the electronic microscope
Roles of Platelet in Hemostasis
1. Activated platelets supply lecithoid
(phospholipid) surface for blood clotting
factor and involve in activating factor X and
prothrombin.
2. Surface of platelet membrane combine with
many blood clotting factor, such as fibrinogen,
FV, FXI, FXIII to speed up coagulation.
Roles of Platelet in Hemostasis
3. Activated platelets release α-granule which
contains fibrinogen to intensify fibrin forming
and blood coagulation.
4. Activated platelets contract clot with its
contractive protein to solidify blood
coagulation.
Mechanism of Platelet in
Hemostasis
Mechanism of Platelet in Hemostasis
Activated Platelets
Release Clotting Compounds
•
•
•
•
•
Adenosine diphosphate (ADP)
Thromboxane A2 and serotonin
Clotting factors
Platelet-derived growth factor (PDGF)
Calcium ions
Platelet Plug: Size Restriction
• Prostacyclin:
– released by endothelial cells
– inhibits platelet aggregation
• Inhibitory compounds:
– released by other white blood cells
• Circulating enzymes: break down ADP
• Negative (inhibitory) feedback: from serotonin
• Development of blood clot: isolates area
The Coagulation Phase
• Begins 30 seconds or more after the injury
Figure 19–12a
Blood Coagulation
Blood Clotting Factor
• Definition: The process of blood flow from
flowing liquid to gel or gelatin.
• Serum: Light yellow fluid after blood
coagulation.
• Difference between serum and plasma mainly
consists in no fibrinogen in serum.
• Blood coagulation is a series of complicated
biochemical reactions with various enzymes.
• Blood clotting factor: Material which are
directly involved in blood coagulation. There
are 12 factors named Roman numerals, except
Ca2+, phospholipid，other factors being
protein, and except FIII (TF), others are in fresh
plasma synthesized by liver with VitK .
• Blood clotting enzymes have two type: inactive
and activated type [FII, FVII, FIX, Fx, FXI, FXII,
FXIII].
Table 19–4
Clotting Factors
•
•
•
•
•
•
•
Also called procoagulants
Proteins or ions in plasma
Required for normal clotting
Fibrin network
Covers platelet plug
Traps blood cells
Seals off area
Cascade Reactions
• During coagulation phase
• Chain reactions of enzymes and
proenzymes
• Form 3 pathways
3 Coagulation Pathways
• Extrinsic pathway: 20-30”
– begins in the vessel wall
– outside blood stream
• Intrinsic pathway: 1-2’
– begins with circulating proenzymes
– within bloodstream
• Common pathway:
– where intrinsic and extrinsic pathways
converge
The Extrinsic Pathway
• Stimulus activates tissue factor (FIII) as
beginning of coagulation.
• Damaged cells release tissue factor (TF)
• TF + other compounds = enzyme
complex
• Activates Factor X
The Intrinsic Pathway
• All blood clotting factors involved in blood
coagulation come from blood. Eyewinker
surface with negative charges (collagenin)
on the endothelium of blood vessel activates
blood FXII as beginning of coagulation
named surface activation.
• Activation of enzymes by collagen
• Platelets release factors (e.g., PF–3)
• Series of reactions activate Factor X
The Common Pathway
•
•
•
•
Enzymes activate Factor X
Forms enzyme prothrombinase
Converts prothrombin to thrombin
Thrombin converts fibrinogen to fibrin
Intrinsic and Extrinsic Coagulation
Pathways
• Terminal steps in both pathways are the same:
– Calcium, factors X and V, and platelet
phosopholipids combine to form prothrombin
activator
– Prothrombin activator converts prothrombin to
thrombin
– This interaction causes conversion of fibrinogen in
fibrin stands that create the insoluble blood clot
Regulation of Blood Coagulation
• Antithrombin III inactivates coagulation
factors and neutralizes thrombin
• When antithrombin III is complexed with
naturally occurring heparin, its action is
accelerated and provides protection against
uncontrolled thrombus formation on the
endothelial surface
• Protein C, a plasma protein, acts as an
anticoagulant by inactivating factors V and VIII
• Humoral anticoagulative system:
1. Amino acid protease inhibitors in blood
include antithrombin III, Cl-inhibitor, α1
antitrypsin, α2 antiplasmin, α2 huge globin,
heparin coenzyme II, protease nexin-1 (PN-1)
to combine with FIXa, FXa, FXIa, FXIIa and
thrombin and then inactivate them for
anticoagulation. Heparin can intensify
functions of antithrombin III.
2. Protein C system are protein C (PC),
thrombomodulin (TM), protein S and Protein
C inhibitors. Main functions of PC consist in ①
It inactivates FVa, FVIIIa with phospholipid and
Ca2+; ②It blocks FXa combining with platelet
phospholipid membrane to reduce
prothrombin activation; ③It stimulates
plasminogen activators release to trigger
fibrinolysis; ④ Protein S is a coenzyme of PC
and greatly intensify functions of PC.
3. Tissue factor pathway inhibitor (TFPI) mainly
coming from vessel endothelial cells inhibits FXa
and inactivates FVIIa-TF complex to block
extrinsic pathway of coagulation with negative
feed back.
4. Heparin used in the clinic widely is due to ①It
combines with antithrombin III to increase
functions of antithrombin III; ②It stimulates
vessel endothelial cell greatlu releasing TFPI and
other anticoagulative material; ③It intensifies PC
activation and stimulates vessel endothelial cell
releasing plasminogen activators to increase
fibrinolysis. [lower molecular weight heparin is
less hemorrhage]
Clotting: Area Restriction
1. Anticoagulants (plasma proteins):
– antithrombin-III
– alpha-2-macroglobulin
2. Heparin” is a natural anticoagulant made by
basophils & mast cells (activates Antithrombin III)
3. Protein C (activated by thrombomodulin)
4. Prostacyclin
Fibrinolysis
• Slow process of dissolving clot:
– thrombin and tissue plasminogen activator (t-PA):
• activate plasminogen
• Plasminogen produces plasmin:
– digests fibrin strands
– Plasmin breaks down fibrin into fibrin degradation
products that act as anticoagulants
Protein S, another plasma protein, accelerates the
action of protein C
• Two fibrinolytic systems:
cellular one and plasma one. The former is
leucocyte, macrophage, endothelial cell,
mesothelial cell and platelet to engulf and
digest fibrin. The latter is plasminogen
activators (PA) and its inhibitors (PAI),
plasminogen, plasmin.
Blood Coagulation and Fibrinolysis
Antifibrinolysis
• Main fibrinolytic inhibitors: They are plasminogen activator
inhibitor type-1 (PAI-1, in platelet), α2-antiplasmin (in liver),
α2-huge globin, α1-antitrypsin, antithrombin III, alexin C1
inhibitor.
• PAI-1 synthesis and release: PAI-1 made by endothelial cell,
smooth muscular cell, mesothelial cell, megakaryocyte is
stored in platelet with inactive form. Some factors such as
thrombin, IL-1, TNFα, etc stimulate its release from platelet.
• PAI-1 function: It inhibits tPA (tissue-type plasminogen
activator) limiting local fibrinolysis of thrombus.
• α2-antiplasmin characteristics: (1) Quick effect, (2) Inhibit
plasminogen adhering to fibrin; (3) Combine with fibrin
αchain and block fibrinolysis
• Clinic relation: Innate deficiency of α2-antiplasmin often
brings about serious hemorrhage.
TERIMA KASIH