Blood
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Basic Principles of Hemostasis
Objectives:
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 Describe the 4 steps of hemostasis
 Describe platelets, their normal count, development, and
functions.
 Describe the process of coagulation
 List the natural anti-coagulants present in blood
 Define hemophilia and list possible symptoms of hemophilia
Steps of Hemostasis
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Hemostasis or haemostasis: is a process which causes bleeding to stop, to
keep blood within a damaged blood vessel.
 The opposite of hemostasis is hemorrhage which is the first stage of
wound healing.
Four steps:
1.
2.
3.
4.
Vascular spasm (vasoconstriction)
Platelet plug formation
Clot formation (blood clotting)
Clot retraction
Platelets
 Platelets (thrombocytes) are minute discs 1 to 4
μm in diameter.
 Formed in the bone marrow from
megakaryocytes,
 The normal concentration of platelets in the
blood is between 150,000 and 400,000 per μL.
COMPONENTS
1. Actin and myosin molecules.
2. Residuals of both the Endoplasmic Reticulum and Golgi apparatus.
3. Mitochondria and enzymes that are capable of forming ATP.
4. Fibrin-stabilizing factor.
5. A coat of glycoproteins that repulses adherence to normal endothelium.
6. Half life of 8 to 12 days.
Platelet or Thrombocyte Physiology
 Shape:
Biconvex disk like,
diameter about 2~4 µm, average
cubage 8 µm3.
 Complicated structure:
under the electronic microscope,
there are α-granule, dense body,
lysin peroxide enzyme, opening
tubular system, dense tubular
system, canaliculus,etc.


Dense body: It contains ADP, ATP, 5-HT, Ca2+, epinephrine, etc.
Origin: Platelet comes from megakaryocyte fractionlet release
in the marrow.
Functions of platelets
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Help in hemostasis (stoppage of bleeding) by:
1.
producing vasoconstriction
2. becoming sticky (activated) to form a platelet plug to close small holes in
blood vessels
3. initiate coagulation
Clinical implications:
Low dose Aspirin reduces platelet adhesiveness:
Rationale for use in “blood thinning”
Low platelet count (< 50,000/μL) causes bleeding disorder
Simple investigation: Bleeding time measurement by finger prick.
Normal bleeding time 3-6 minutes
Disease when platelet count is low: Thrombocytopenic purpura
Platelet Plug
When
platelets come in contact with a damaged vascular
surface, they immediately change their own characteristics.
•
•
•
•
•
•
•
Begin to swell;
Assume irregular forms with numerous irradiating pseudopods;
Release granules that contain multiple active factors;
Become sticky and adhere to collagen in the tissues and to a protein
called von Willebrand factor that leaks into the traumatized tissue
from the plasma;
Secrete large quantities of ADP;
Enzymes form thromboxane A2.
ADP and thromboxane in turn act on nearby platelets to activate
them as well.
Inactive Platelet
Under the electronic microscope
Activated Platelet for Hemostasis
Under the electronic microscope
Blood coagulation: factors involved
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Physiological Hemostasis
 *Definition: The process from vessel bleeding to automatic hemostasia.
 *Bleeding
time: The time from vessel bleeding to automatic
hemostasia. Normal time is 1~3 min and it is longer when platelet decrease.
 * Process of hemostasis:
1. Blood vessel contraction or convulsion (induced by neuroreflex; 5hydroxytryptamine (5-HT); thromboxane A2 (TXA2); endothelin (ET ).
1. Platelet thrombosis forming (made by platelet adhesion, aggregation,
release and contraction).
2. Fibrin, clot forming and maintenance (made by blood coagulation
activation).
Hemostasis:
BV Injury
Tissue
Factor
Neural
Blood Vessel
Platelet
Coagulation
Constriction
Activation
Primary hemostatic plug
Activation
Reduced
Plt-Fusion
Blood flow
Thromibn,
Fibrin
Stable Hemostatic Plug
Physiological Hemostasis
Endocrine functions of vessel endothelial cells
 Materials 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.
 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).
 Promoting coagulative material: Tissue factor, vWF, blood clotting
factor V, plasminogen activator inhibitor (PAI-1, PAI-2, ATIII), TNFα,
interleukin-1 (IL-1).
 Vessel constricting and relaxing modulators: endothelin-1 (ET-1),
EDRF (NO), PGI2, etc.
Roles of Vessel Endothelial Cells in the Hemostasis
Roles are close related to its endocrine functions
① Vessel endothelium serves as barrier between under endothelial
structure (namely, collagen) and blood. As soon as collagen expose to
blood, hemostasis of platelet is immediately activated to form
thrombus blocking wounded vessels.
① Platelet activation can releases constrictive factors (TXA2, ET-1, 5HT, etc) making vessel convulsion, lasting about 60 sec.
① 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.
Physiological Characteristics of Platelets
 Thrombocyte adhesion: its membrane glycoprotein (GP, GPIb/IX
and GPIIa/IIIb), collagen (underendothelial structure), vWF (plasma
component), fibrinogen are involved in 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.
 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.
Roles of Platelet in Hemostasis
 Activation of platelet: Stimulus brings about thrombocyte adhesion,
aggregation, release and contraction.
 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.
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(1) of Platelet in Hemostasis
Mechanism(2) of Platelet in Hemostasis
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).
Blood Coagulation
 Intrinsic pathway of blood coagulation: 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 F actor XII as beginning of coagulation named surface activation.
 Extrinsic pathway of blood coagulation: Stimulus activates tissue factor
(FIII) as beginning of coagulation.
Extrinsic pathway of blood coagulation is faster than intrinsic pathway of
blood coagulation because its steps are more simple.
 *Basic steps of blood coagulation [typical positive feedback]:
Prothrombin activator forming [FXa-Va-Ca2+-phospholipid] Step 1
Prothrombin
thrombin
Step 2
Fibrinogen
fibrin (clot)
Step 3
 Hemophilia A, B, C in the clinic results from deficiency of FVIII, FIX,
FXI in the blood, respectively.
HEMOSTATIC SYSTEM
INTRINSIC
EXTRINSIC
PATHWAY
PATHWAY
COMMON PATHWAY
Thrombin
Fibrinogen
Fibrin
PLATELETS
CLOT
COLLAGEN
TISSUE FACTOR
VESSEL WALL
Mechanism of Blood Coagulation
Anticoagulative system in blood
1-Serine protease inhibitors: inhibit the coagulation cascade.
2-Neutralizers of activated coagulation factors (components of protein
C system)
1-Serine protease inhibitors:
1-Antithrombin (III).
2-Heparin and heparin like substance.
3-Alpha 1 antitypsin.
4-Alpha 2 macroglobulin
2-Neutralizers of activated coagulation factors :
1-Protein C: synthesized in the liver, vit. K dependant, activated by thrombin.
2-Thrombomodulin.
3-Protein S and C4b-binding
Specific inhibitors of clotting factors
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1.Antithrombin III
 It is a plasma protein that inactivates thrombin by forming an
irreversible complex with it.
 It resembles alpha 1-antitrypsin except that it inhibits thrombin
much more strongly than it inhibits elastase.
 Also, it blocks other serine proteases in the clotting cascade
namely, factors XIIa, XIa, IXa, and Xa.
2.Heparin
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 The inhibitory action of antithrombin III is enhanced by heparin
 It is
a negatively charged polysaccharide found in mast cells
near the walls of blood vessels and on the surfaces of
endothelial cells
 Heparin acts as an anticoagulant by increasing the rate of
formation of irreversible complexes between antithrombin III and
the serine protease clotting factors.
 Antitrypsin and antithrombin are serpins, a family of serine
protease inhibitors.
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Electron Micrograph of a Mast Cell. Heparin and
other molecules in the dense granules are released
into the extracellular space when the cell is
triggered to secrete.
3. Alpha 1-antitrypsin
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 which normally inhibits elastase
 alpha 1-Antitrypsin activity normally increases markedly
after injury to counteract excess elastase arising from
stimulated neutrophils.
 The mutant a 1-antitrypsin caused the patient's thrombin
activity to drop to such a low level that hemorrhage ensued.
Fibrinolysis

Definition: is the process wherein a fibrin clot, the product of
coagulation, is broken down (clot retraction). Its main enzyme plasmin
cuts the fibrin mesh at various places, leading to the production of circulating
fragments that are cleared by other proteases or by the kidney and liver
Disorders and Diseases of blood coagulation
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1- Hemophilias: are the best-known coagulation factor
disorders.
The three main forms are:
Hemophilia A
(factor VIII deficiency)
Hemophilia B
(factor IX deficiency or "Christmas
disease")
Hemophilia C
(factor XI deficiency,
mild bleeding tendency).
2. von Willebrand disease
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 It is the most common hereditary bleeding disorder and is
characterized as being inherited autosomal recessive or
dominant.
 In this disease there is a defect in von Willebrand factor
(vWF) which mediates the binding of glycoprotein Ib
(GPIb) to collagen.
 This binding helps mediate the activation of platelets and
formation of primary hemostasis.
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3. Deficiency of Vitamin K
 may also contribute to bleeding disorders because
clotting factor maturation depends on Vitamin K.
4. Liver diseases:
 Some clotting factors; II, IX, VII, X are synthesized
in liver
 Liver diseases
deficiency of these factors
bleeding disorders.