PHYSIOLOGY

OF

BLOOD COAGULATION

H E M E O S T A S I S

•The fluidity of the blood is a consequence of

the balance between two processes:

1. blood coagulation (clot formation)

2. blood fibrinolysis (clot dissolution)

•Hemostasis consists of coagulation and

fibrinolysis.

H E M E O S T A S I S

•Coagulation prevents the blood loss from a damaged

blood vessel. It keeps blood within a damage vessel.

•It is the innate response for the body to stop bleeding

and loss of blood.

•Fibrinolysis is a process necessary for clot

dissolution. It prevents blood clots from growing and

becoming problematic.

H E M E O S T A S I S

Three inherent mechanisms contribute to

hemeostasis

Vascular constriction

Formation of platelet plug

Blood coagulation (plasma clotting

factors)

VASCULAR SPASM

Immediately after a blood vessel has been cut or

ruptured, the trauma cause the vessel to contract

and reduce the blood flow.

The contraction results from:

activation of sympathetic nervous system

local humoral factors from the traumatized

tissues and blood platelets (serotonin, epinephrin

tromboxane A2).

Trauma activates sympathetic nervous system what

causes the vessel to contract and reduce the blood flow.

PLATELETS

•Platelets, are also called thrombocytes, are large fragments

from the cytoplasm of bone marrow cells called

megacariocytes.

•Platelets lack a nukeus and cannot reproduct, they have

mitochondrias and enzyme systems capable of producing ATP

and prostaglandins, which are required for their function in

hemostasis.

•The newly formed platelets released from bone marrow spend

up to 2 days in the spleen before they are released into the

blood (1/3 of platelets remains in the spleen, 2/3 is circulating

in the blood).

PLATELETS

•Platelet production in bone marrow is controlled

by a protein called thrombopoetin that causes

proliferation and maturation of megacariocytes.

•The sources of thrombopotin are: the liver, kidney,

smooth muscle and bone marrow.

•Thrombopoetin production is regulated by the

number of platelets in the circulation.

VASCULAR STRUCTURE

Internal membrane

(intima)

Medial membrane

(media)

External

membrane

(adventitia)

endothelium

Basement membrane (collagen)

Elastic membrane (elastin, collagen, fibronectin, GAG)

Vascular

smooth muscle

cells

External elastic membrane(elastin, collagen)

Figure made by prof. Krzysztof Książek

FORMATION OF THE PLATELET

PLUG Platelets adhere to the injured area of the vessel wall,

especially to the injured endothelial cells and to exposed collagen (bridged by von Wiellebrand’s factor( vWF).

Immediately after adhesion they change their characteristic drastically and secret large quantities of ADP, tromboxane A2, which in turn act on nearby platelets to activate them.

Damaged vascular walls elicit activation of increasing number of platelets, that themselves attract more and more

platelets thus forming a platelet plug.

Platelets adhere to the injured area of the vessel wall,

especially to the injured endothelial cells and to exposed

collagen (bridged by von Wiellebrand’s factor( vWF).

Immediately after adhesion platelets change their

shape drastically and secret large quantities of ADP,

tromboxane A2, which in turn act on nearby platelets

to activate them.

PLATELETS

•Platelets contain two specific type of granules – alpha, and

delta.

•Alpha granules release mediators for hemostasis (plasma

cloting factors: I, V, VII, vWF), and growth factors , which

cause vascular endothelial cells, smooth muscle cells and

fibroblast to proliferate and growth.

•Delta granules (or dense granules) contain ADP, Ca 2+,

serotonin and epinephrin → platelet agregation and

vasoconstriction.

Ivy method - 4-8 min

In the Ivy method the blood pressure cuff is

placed on the upper arm and inflated to 40

mm Hg. A disposable lancet is used to make a

shallow incision that 1mm deep on the

underside of the forearm.

BLEEDING TIME

Laboratory evaluation of blood vessels and PTLs

Plasma clotting factors II

Most clotting factors normally are not active.

Their activation requires a cascade of events. One

active clotting factor activates another.

Factors II (prothrombin), VII, IX, X, need vitamin K

as an essential cofactor for their formation in the liver.

Ca2+ ions are required for several steps in the clotting

process.

BLOOD COAGULATION

MECHANISM OF COAGULATION

Two conditions can lead to blood clotting:

1. Blood vessels damage (collagen fibers – initiate

intrinsic pathway).

2. Damage to cells which build the vessel wall

(tissue factor – initiates extrinsic pathway).

Intrinsic and extrinsic pathways initiate the

conversion of prothrombin to trombin.

MECHANISM OF COAGULATION

Trombin is an enzyme that enzymatically causes

polymeryzation of plasma fibrinogen (soluble protein) into

the fibrin threads (insoluble protein) that lead to blood

clotting.

Fibrin threads entrap large numbers of RBCs, WBCs,

platelets and plasma to form a soft gelatinous mass- the

blood clot.

Platelet aggregation is enhanced by thrombin.

BLOOD COAGULATION

Laboratory evaluation of plasma clotting

factors

Within 3-6 minutes after rupture broken

ends of vessel are filled with clot.

Conversion of fibrinogen to fibrin under

the trombin condition is the clotting

process.

COAGULATION TIME Laboratory evaluation of plasma clotting factors

APTT – Activated Partial Tromboplastin Time

(Intrinsic pathway and Common Pathway) – 25-40 s

INR- International Normalized Ratio 0.8-1.2

(Extrinsic Pathway and Common Pathway)

TT –Trombin Time – 15-19 s

(conversion of fibrinogen to fibrin)

COAGULATION TIME

APTT

TT

INR

CLOT DISSOLUTION

The clots must be removed in order to prevent

permanent obstruction.

Plasmin is a proteolytic enzyme that digests fibrin.

It is synthesized from its precursor plasminogen.

Residue of the clot dissolution is removed by the

phagocytic WBCs .

TROMBOPROTECTION I

It is necessery to prevent

excessive clotting and occlusion

of major blood vessels (e.g.,

coronary artery - thrombosis)

and embolisms due to clot

migration.

TROMBOPROTECTION II

1. T R O M B I N I N H I B I T I O N

Antytrombin III – the most important tromboprotective plasma

protein (inactivates also plasma clottinf factors XI, XII)

Heparin (inactivates plasma clottinf factors II, X)

2. C L O T T I N G F A C T O R S I N H I B I T I O N

Protein C and S (vit K dependent) – inhibit factor V, VIII

Vitamin K antagonists (cumarin derivates as warfarin, acenocoumarol)

3. P L A T E L E T I N H I B I T I O N

Prostacyklin (PGI2– inhibits platelets adhesion to normal

endothelium)

Aspirin – inhibit platelets aggregation by blocking TXA2 production by

inhibition of COX-1 and COX-2)

BLOOD

PATOPHYSIOLOGY

BLEEDING DISORDES

BLEEDING DISORDERS

Hemorrhagic diathesis (HD) can be caused by:

Disorders of thrombocytes (thrombocytic HD)

Vascular defects ( vascular HD)

Disorders of the plasma clotting factors (plasma HD)

BLEEDING DISORDERS - SYMPTOMS

Thrombocytic and vascular HD

Ecchymosis and bleeding into the skin (petachiae)

Dermatomes (bruises)

Epistaxis (nosebleeds)

Gastrointestinal, genitourinary and central nervous system

bleeding

Intracranial bleeding (rare, life-threatening)

Plasma HD

Bleeding into joints (large joints in leg), muscles bleeding

(bruises), body cavities bleeding (e.g. pleural cavity,

peritoneal cavity)

petachiae

PLATELET HD I

ACQUIRED THROMBOCYTOPHENIAS (TCP’s)

(Most common HD)

life-threatening symptom: intracranial bleeding (↓20 000/µl PLTs)

Idiopathic thrombocytophenia purpura

(1-3 weeks after viral infection) shortens platelets’ survival due to immune

complex

Diminished platelet formation

aplastic anemia

bone marrow tumors

cobalamine or folate deficiency

Increase platelets destruction

vascular prostheses

artificial valves

Platelets sequestration

enlarged spleen

PLATELET HD II

ACQUIRED THROMBOCYTOPATHIES

(qualitative disorders)

Uremia (diminished platelets adhesion)

Acetylosalicylic acid (ASPIRIN) - used in thrombosis

prophylaxis

Aspirin is a cyclooxygenase inhibitor and causes decreased tromboxane A2

production (vasoconstrictor, aggregation factor)

•Aspirin irreversibly blocks the COX-1 in thrombocytes.

•We should wait for a new platelets for about 1 week, after discontinuation

of therapy

PLASMA HD I

HEREDITARY COAGULOPATHIES

Classical hemophilia A (absence or reduced formation or

defect of factor VIII)

Hemophilia B (IX) = Christmas Disease

Hemophilia C (XI)

Rare homozygous deficiency of factor I (fibrinogen),

II (prothrombin), V, VII, X, XIII

von Willebrand’s disease

HEMOPHILIA A I

The most common of the X-chromosomal recessive form

(one in 10 000 newborn boys)

Women are carriers of the X-chromosom related gene.

Males and homozygotous females (extremely rare) suffer

from hemophilia

bleeding sites are:

- muscles (bruises)

- body cavities (e.g. peritoneal cavity)

- large joints of the leg becoming markedly deformed with

time (hemophilic arthropathy)

HEMOPHILIA A II

The degree of bleeding is related to the amount of factor

activity and the severity of the injury

Spontaneous bleeding is seen with factor activity levels

below 1 % (severe hemophilia)

About 5% activity level for factor VIII is usually enough

for normal living, but not enough when trauma occurs

(mild hemophilia)

von WILLEBRAND’S DISEASE

von Willebrand factor (vWF) is a large multimeric glycoprotein present

in blood plasma and produced in endothelial cells, megakariocytes,

platelets, and subendothelial connective tissue

von Willebrand factor binds to plasma clotting factor VIII, protects it

against inactivation and it is important in platelets agreggation and

adhesion to wound sites

von WILLEBRAND’S DISEASE

Autosomal dominant trait occurring in males and females

In von Willebrand’s disease, both a factor VIII and von Willebrand

factor deficiency exist

The patients suffered from plasma HD ( lack of VIII plasma factor) and

platelets HD (lack of von Willebrand factor = platelets adhesion defect)

Clinical manifestation are typical for platelets HD ;

-deep tissue bleeding (bruises, petachiae)

-Gastrointestinal, genitourinary bleeding (prolonge menstrual bleeding)

- arthropaty (rare)

- peritoneal and intracranial bleeding (rare, life-threatening)

PLASMA HD

AQUIRED COAGULOPATHIES

Liver damage (e.g. liver cirrhosis)

Deficiency or inhibition of vitamin K

• malabsorbtion, malnutrition

• destruction of saprpphytic bacteria by antibiotics of the intestinal flora

• drugs – inhibition by the cumarine derivates (e.g. warfarin,

acenocumarol); is use for oral prophylaxis of thrombosis (anticoagulant

treatment)

Consumption coagulopathy (disseminated intravascular

coagulation DIC)

DISSEMINATED INTRAVASCULAR

COAGULATION (DIC) I

It is a coagulation disorders caused by acute

or chronic activation of thrombin with clot

formation and platelets activation that

secondary results in activation of fibrynolysis

and bleeding (heart failure, acute kidney

failure, circulatory shock)

DISSEMINATED INTRAVASCULAR

COAGULATION (DIC) II

C A U S E S

Cell damage releases large amount of tissue tromboplastin

and initiation of extrinsic clotting pathway (VII plasma

cloting factor)

neoplasm (e.g leukemia)

massive trauma ( e.g. burns, ABO blood mismatches)

Damage of vascular wall and initiation of intrinsic clotting

pathway (XII plasma cloting factor)

- vasculitis

- sepsis (whole-body inflammation caused by inflammation)

- scirculatory shock

← vascular wall damage and exposure of

collagen fibers

← cell damage

and release of

TF

DISSEMINATED INTRAVASCULAR

COAGULATION (DIC) III

P A T O M E C H A N I S M

1. Activation of clotting mechanism

a. tissue tromboplastin (extrinsic clotting pathway)

b. vascular wall damage →endothelial cells’ injury (intrinsic

clotting pathway)

2. Coagulation factors are consumed and depleted

3. Clot occludes the blood vessels and causes tissue ischemia

4. Concomitantly the fibrinolitic system is activated

5. Large number of fibrin and fibrinogen degradation products

impaired fibrin polymerization and platelets activation caused

bleeding → CIRCULATORY SHOCK