HEMOSTASIS (blood clotting, stop of bleeding)
= set of mechanisms which prevent bleeding on one
side and stop already existing bleeding on the other
side.
• Reaction of vessels
• Actions of platelets
• Blood clotting
HEMOSTASIS (blood clotting, stop of bleeding)
Ideal balance of several systems:
• endothelium of vessel wall
• collagen below endothelium
• tonus of the vessels
• number and quality of platelets
• clotting and fibrinolytic systems
• character of blood flow in the vessel
prevents bleeding on one side and intravascular blood
clotting on the other side.
REACTION OF VESSELS
Vasoconstriction.
Vasoconstriction depends on the severity of vascular
injury.
Serotonin (granules in platelets).
Adrenalin.
Fibrinopeptides.
PLATELETS (THROMBOCYTES)
Nucleus-less, colorless, granulated, the smallest formed
elements in blood.
Origin: megakaryocytes of bone marrow under the effect of
colony stimulating factors – interleukins (IL-1, IL-3, IL-6) and
granulocytes and macrophages stimulating factor (GM-CSF)
Number: 200 000 – 500 000 in ml, one third in lien and two
thirds in peripheral blood
No age and gender differences in platelet count.
Trombocytosis – after splenectomy.
Size: 2 – 4 mm in diameter, 0,5 – 1 mm thickness, 4 – 8 fl
volume
Shape: smooth, round discs
The shape is kept by cytoskeleton (disk of microtubules
around the periphery, invaginated membrane, canalicular
system connected to extracellular space).
Membrane: contains receptors for adhesion to certain
surfaces, e.g. collagen, von Willebrand factor, fibrinogen
Cytoplasm: contains actin, myosin, glycogen, lysozomes
and
Granules: dense granules (non-protein substances –
serotonin, ADP, adenonucleotides) and a granules
(protein substances - clotting factors, platelet derived
growth factor – PDGF)
Glycocalyx: 10 – 50nm, mixture of proteins and
mucopolysaccharides (clotting factors, ions, amino acids,
histamin, drugs…)
Life span: 9 – 12 days, biological half-time – about 4 days
Jurk K, Kehrel BE: Platelets: Physiology and biochemistry. Seminars in Thrombosis and Hemostasis
2005, 31(4):381-392.
Function of platelets
• Protection of organism from blood loss
• Keeping the integrity of vessel wall and healing of the
ruptured vessel (PDGF from a-granules)
• Inflammatory reactions, changes in permeability of
capillaries, removing of xenogenous substances, viruses,
bacteria, graft rejection …
• Carrier for many substances absorbed to platelets surface
HEMOSTASIS I. – white clot
Adhesion (exposure of the vessel wall – collagen – receptors for collagen on
platelet, laminin, von Willebrand factor).
Activation and change of shape – collagen, ADP, thrombin. Glycoprotein
IIb/IIIa receptors.
Secretion (degranulation):
Stimulation of aggregation – ADP
Stimulation of adhesion – vWF and fibronectin
Vasoconstriction – serotonin, tromboxane A2
mitogenic effects – growth factor (PDGF)
activation of platelets and phagocytes – PAF (cytokine, G-coupled receptor,
phospholipase C, DAG, increase of intracellular Ca2+concentration, phospholipase A2 –
arachidonic acid – thromboxane A2)!!! Therapeutic use of acetylsalicylic acid!!!
Aggregation.
Vasoconstriction.
Convolution of inner layer of vessel wall (at the place of rupture).
ADP
Ca++
Serotonin
Vasoconstriction
Noradrenalin
Dense granules Alpha granules
Fibrinogen
PDGF atherosclerosisvWF
V XIII
vWF
Collagen
Endothelium
Thromboxan A2
AA
COX-1
PGH2
Aspirin
Vasoconstriction
Activation
Inhibition
Ticlopidine
ADHESION
Inhibition
Fibrinogen
Receptor IIb/IIIa
Abciximab
vWF
AGGREGATION
Jurk K, Kehrel BE:
Platelets: Physiology and
biochemistry. Seminars in
Thrombosis and
Hemostasis 2005,
31(4):381-392.
Broos K, De Meyer SF,
Feys HB,
Vanhoorelbeke K,
Deckmyn H: Blood
platelet biochemistry.
Thrombosis
Research 2012,
129(3):245-249.
Jurk K, Kehrel BE: Platelets: Physiology and biochemistry. Seminars in Thrombosis and Hemostasis
2005, 31(4):381-392.
 Activation of PLC  PIP2
cleavage to IP3 and DAG
 IP3 mobilizes Ca2+ from ER
 Ca2+ 
 1. activation of PLA2 
activation of arachidonic
acid pathway   TXA2 =
 degranulation
 2. activation of MLCK
(Myosin light-chain kinase)
  contraction of
contractile elements
  platelet shape
change
  degranulation
 DAG activates PKC  
degranulation
Processes in platelets after „activation“ of receptors
Jurk K, Kehrel BE:
Platelets: Physiology
and biochemistry.
Seminars in
Thrombosis and
Hemostasis 2005,
31(4):381-392.
Silverthorn, D. U. Human Physiology – an Integrated Approach. 6th. edition. Pearson Education, Inc. 2012.
Jurk K, Kehrel BE: Platelets: Physiology and biochemistry. Seminars in Thrombosis and Hemostasis
2005, 31(4):381-392.
Coughlin SR: Thrombin signalling and protease-activated receptors. Nature 2000, 407(6801):258-264.
HEMOSTASIS II. – red clot
Prothrombin (factor X) – thrombin.
Fibrinogen – fibrin monomer – fibrin polymer (factor III, Ca2+).
Intrinsic pathway – extrinsic pathway of factor X activation.
Jurk K, Kehrel BE:
Platelets: Physiology
and biochemistry.
Seminars in
Thrombosis and
Hemostasis 2005,
31(4):381-392.
Figure 36-2 Schema for conversion of prothrombin to thrombin and polymerization of fibrinogen to form fibrin fibers.
Downloaded from: StudentConsult (on 15 June 2006 03:00 PM)
© 2005 Elsevier
Figure 36-3 Extrinsic pathway for initiating blood clotting.
Downloaded from: StudentConsult (on 15 June 2006 03:00 PM)
© 2005 Elsevier
Figure 36-4 Intrinsic pathway for initiating blood clotting.
Downloaded from: StudentConsult (on 15 June 2006 03:00 PM)
© 2005 Elsevier
Silverthorn, D. U.
Human Physiology –
an Integrated
Approach. 6th. edition.
Pearson Education,
Inc. 2012.
TF, tissue factor TFPI, tissue factor pathway inhibitor
CLOTTING MECHANISM
Activated platelet membrane
Jurk K, Kehrel BE: Platelets:
Physiology and biochemistry.
Seminars in Thrombosis and
Hemostasis 2005, 31(4):381-
392.
Silverthorn, D. U. Human Physiology – an Integrated Approach. 6th. edition. Pearson Education, Inc.
2012.
FIBRIN FORMATION AND DEGRADATION
Fibrinogen
Fibrin
FDPs
FDPs, fibrin degradation products
Silverthorn, D. U. Human
Physiology – an
Integrated Approach.
6th. edition. Pearson
Education, Inc. 2012.
SUMMARY
Silverthorn, D. U. Human Physiology – an Integrated Approach. 6th. edition. Pearson Education, Inc. 2012.
SUMMARY
Factor Name of factor Biological half-time (h)
I fibrinogen 120-144
II prothrombin 48
III thromboplastin, thrombokinase very short
IV calcium ions
V proaccelerin 12-15
VII (AHF) proconvertin, stabile factor 2-5
VIII antihaemofilic factor A, a. globulin 5-12
IX Christmas factor, antihem. f. B 12-30
X Stuart-Prower factor 32
XI antihaemofilic factor C, PTA less than 12
XII Hageman factor less than 12
XIII factor stabilising fibrin 48-72
HMW-K Fitzgerald f. (high-molecular-weight kininogen)
Pre-K prekallikrein
Ka kallikrein
PL Platelet phospholipids
Silverthorn, D. U. Human Physiology – an Integrated Approach. 6th. edition. Pearson Education, Inc. 2012.
INTRAVASCULAR COAGULATION
Damage of epithelium caused by:
1) Atherosclerosis (myocardial infarction, stroke)
2) Inflammation (venous thrombosis, pulmonary
embolism)
THROMBOSIS
EMBOLISM
damaged endothelium
damaged endothelium
Thrombus
Embolus
Example:
MI
Stroke
Example:
Pulmonary embolism
Antithrombotic drugs
• We influence function of thrombocytes, not number of
throbocytes!
• Primary and secondary prevention of atherothrombosis
– Acute Coronary Syndromes (ACS)
– Cerebrovascular Ischemic Attack
– Peripheral arterial disease (PAD)
• antiplatelet agents?
• Inhibitors of cyklooxygenase/inhibitors of thromboxane A2 synthesis
or antagonists of the receptors
• Inhibitors of ADP receptors (P2Y12)
• Antagonists of protease-activated receptors (PAR-1)
• Antagonists of surface glycoproteins (GP IIb/IIa)
• Blockage of serotonin pathway
• Other mechanisms
Angiolillo DJ, Ferreiro JL:
Platelet Adenosine
Diphosphate P2Y(12)
Receptor Antagonism:
Benefits and Limitations
of Current Treatment
Strategies and Future
Directions. Revista
Espanola De Cardiologia
2010, 63(1):60-76.
CONTROL OF HAEMOCOAGULATION
Clotting is counteracted by anti-coagulating mechanisms:
Non-humoral control:
Endothelial surface factors.
Blood stream: restriction of increase of clot, dilution and
removal of clotting factors.
Interaction between thromboxane A2 and prostacycline.
Humoral control:
Fibrin: binds thrombin strongly – „antithrombin“
Antithrombin III: circulating inhibitor of proteases (active
forms of factors IX, X, XI, XII), binding of proteases of
clotting system is facilitated by heparin from mast cells (cofactor
of heparin)
Thrombmodulin: thrombin binding protein, produced by
endothelial cells.
Thrombin + Thrombmodulin = activator of protein C
Protein C: inactivation of factors V and VIII
Inhibition of the inhibitor of activator of tissue
plasminogen (= more plasmin – degradation of fibrin)
Plasmin (fibrinolysin): active part of fibrinolytic system.
Precursor: plasminogen, catalyzed by thrombin and tissue
activator of plasmin (TPA) – use in therapy of myocardial
infarction!!! Streptokinase.
Ezihe-Ejiofor JA, Hutchinson N:
Anticlotting mechanisms 1: physiology
and pathology. Continuing Education in
Anaesthesia, Critical Care & Pain
Advance Access 2013
Kauskot A, Hoylaerts
MF: Platelet receptors.
Handbook of
experimental
pharmacology
2012(210):23-57.
FIBRINOLYSIS
Inactive plasminogen.
Active plasmin (fibrinolysin).
Activators of plasminogen.
Inhibitors of plasminogen.
Thrombolysis
UPA, urokinase plasmin activator tPA, tissue plasmin activator
PAI, plasmin acivator inhibitor alpha2PI-Plasmin, complex
ANTI-CLOTTING TREATMENT
Defibrination: removal of fibrin (substances from snake
poisons) – in vitro
Decalcification: binding or removal of calcium ions (sodium
citrate, potassium or ammonium oxalate) – in vitro
Heparin: natural anticoagulant, mast cells, active only in the
presence of antithrombin III, used also in vivo
Cumarin derivatives (dicumarol, warfarin): inhibition of
effects of vitamin K in liver – disorders of factors II, VII, IX, X,
protein C, protein S (facilitates activation of Va and VIIIa via
protein C)
Hirudin: obsolete, salivary glands of leech (Hirudo
medicinalis)
Anticoagulants
Heparin antithrombin III
test: aPTT,
antifactor Xa level
Inhibition
Activation
In vivo:
Coumarin (warfarin)
Vitamin K Hepar prothrombin
Liver
In vitro: Heparin antithrombin III
Sodium citrate Ca++
test: PT
INR=PTpatient/PTnorm
warfarin INR 2-3
aPTT: activated partial thromboplastin time PT: prothrombin time
HMWK, high-molecular-weight-kininogen PK, prekallikrein F, factor
Tests aPTT and PT
Prothrombin time test
Activated Partial Thromboplastin Time test
Figure 36-5 Relation of prothrombin concentration in the blood to "prothrombin time."
Downloaded from: StudentConsult (on 15 June 2006 03:00 PM)
© 2005 Elsevier
STREPTOKINASE
CLOTTING DISORDERS
Clotting diseases = disorders, in which blood clotting starts
either spontaneously or after inadequately small stimulus.
Blood clotting disorders caused by diseases of vessels
Disorders of platelets:
1)thrombocytopenia
2)thrombocytopathy
Coagulopathy – loss or lack of plasmatic clotting factors:
1)Disorders of synthesis: hereditary (haemophilia),
attained (hypo-vitaminosis K, therapy with derivatives of
cumarin)
2)Disorders of metabolism:
•consumptive coagulopathy and hyperfibrinolysis
•repeated transfusions
•immunocoagulopathy
•therapy by heparin
•paraproteinemia