Second

Section 3 Hemostasis Coagulation Fibrinolysis

Hemostasis  Definition:

The process the body uses to stop the flow of blood when the vascular system is damaged. Prevention of blood loss.

Mechanisms of Hemostasis:   



Vascular spasm Formation of a platelet plug Formation of a blood clot as a result of blood coagulation Eventual growth of fibrous tissue into the

§1. Vascular Constriction 



The trauma to the vessel wall itself causes the vessel to contract. (instantaneously) Contraction causes: 1. 2. 3.

Nervous reflexes Local myogenic spasm (Most) Local humoral factors from the traumatized tissues and platelets (Most for smaller vessels)

§2. Formation of a platelet plug If the rent in the blood vessel is very small, it is often sealed by a platelet plug, rather than by a blood clot.

Platelet Damaged vascular surface (eg. Collagen fibers)

Swell

Protrude Contractile Become Secrete Form Thromboxane irradiating protein sticky Adenosine pseudopods contract diphosphate A2 (TXA2) (ADP) Release granule Adhere to containing Collagen and active factors Von willebrand (fibrin-stablizing factor, factor (vWF) growth factor, etc)

§3. Blood Coagulation in the Ruptured Vessel In 15 to 20 seconds: clot begins to develop. (if the trauma to the vascular wall has been severe) Or in 1 to 2 minutes. (if the trauma has been minor)  Within 3 to 6 minutes: filled with clot.  After 20 minutes to an hour: clot retract 

§4. Fibrous Organization or Dissolution of the Blood Clot 

Two courses of blood clot: Invaded by fibroblasts.  Dissolve. 





Fibroblasts invasion: within a few hours. Organization of the clot into fibrous tissue: within 1 to 2 weeks.

Blood Coagulation  Definition  a process in which liquid blood is changed into a semisolid mass (a blood clot)

Coagulation Factors Name

Factor I

Fibrinogen

Plasma halflife (h)

纤维蛋 72 - 96

白原

II

Prothrombin

凝血 60

酶原

III

Tissue Factor or thromboplastin 组织 因子

IV V

Ca++ Proaccelerin

前加 15

速素

VII

Proconvertin 素

前转变 5

Name

Factor IX

Plasma half-life (h)

Antihemophilic B factor or 25 Christmas factor 血浆凝血激 酶

X XI

Stuart or Stuart-Prower 40 factor Plasma thomboplastin 45-65 antecedent 血浆凝血激酶前质子

XII

Hageman factor, contact factor 接触因子

XIII

Fibrin stabilizing factor 纤维 150 蛋白稳定因子

60

Three essential steps of Clotting 

Formation of prothrombinase complex (prothrombin activator)



Prothrombin (FII) activated



Formation of fibrin (Ia)

§1. Initiation of coagulation: Formation of Prothrombin activator Trauma to the vascular wall and surrounding tissues; Trauma to the blood itself

Extrinsic pathway Intrinsic pathway

Prothrombin activator: factor Xa-Va

Prothrombin activator

Intrinsic Pathway 

Intrinsic Pathway is defined as a cascade that utilizes only factors that are soluble in the plasma.

Contact with the collagen under subendothelial cell

Extrinsic Pathway 

Extrinsic Pathway triggered by tissue damage, which cause the release of factor III （ Tissue Factor ）

Contact with the collagen under subendothelial cell

§2. Conversion of prothrombin to thrombin 



(FII) (FIIa) The rate-limiting factor in causing blood coagulation is the formation of prothrombin activator. Platelets’ role in FII→FIIa. Platelets adhere to the damaged tissue, and provide prothrombin receptors to bind with prothombin. This binding accelerate the conversion and localize the formation of thrombin.

§3. Conversion of fibrinogen to fibrin --formation of the clot 

Action of thrombin on fibrinogen to form fibrin. 

Thrombin acts on fibrinogen to remove four peptides from each molecule of fibrinogen, forming a molecule of fibrin monomer. F



Thrombin activate fibrin-stabilizing factor ( plasma globulins, platelets) which promote the formation of Cross-linked fibers. F

Formation of fibrin

Prothrombin (II) Prothrombin activator

Ca2+

(Xa-Va)

Thrombin (IIa) Fibrinogen (I)

Fibrinogen monomer Ca2+ Fibrin fibers

Thrombin activated fibrin-stabilizing factor Cross-linked fibrin fibers

Summary 

The classical model of blood coagulation involves a series (or "cascade") of zymogen activation reactions.



Coagulation can be initiated via the “intrinsic” or “extrinsic” pathway.

Summary 

 

Both the intrinsic and the extrinsic pathways proceed through a common pathway by forming activated factor X (factor Xa-Va-Ca2+ Prothombin Activator) Amplification of coagulation reactions. The intrinsic and the extrinsic pathways are highly interconnected.

Vicious circle of clot formation (Amplification of coagulation)



Most important cause: thrombin act on many blood-clotting factors in addition to fibrinogen.  Prothrombin  Other blood-clotting factors responsible for the formation of promthrombin activator, eg, VIII, IX, X, XI and XII  Aggregation of platelets.

 Amplification of coagulation FIIa activate FXI.  Intrinsic pathway interconnect with extrinsic pathway TF-VIIa complex activate FIX.

Factors That Affect Coagulation 

Procoagulants

More than 50 kinds in blood



Anticoagulants



Whether blood will coagulate depends on the balance between Procoagulants and Anticoagulants.



In the blood stream, the anticoagulants normally predominate.



The reasons that blood can flow through vessels fluently are as follows:  There

is no injury in blood vessel.

 Most

of clotting factors are present in blood with inactive state.

 There

are some anticoagulants (Compounds that do not allow blood to clot) exist in blood.

Anticoagulative factors 1.

Endothelial surface factors: (1) the smoothness of the endothelial surface (2) a layer of glycocalyx on the endothelium. (3) thrombomodulin bound with endothelial membrane, which binds with thrombin.

Thrombomodulin - thrombin complex Remove thrombin

Protein C (anticoagulant) FVa, FVIIIa activate

inactivate

Anticoagulative factors 2.

Antithrombin action of fibrin and antithrombin III. Both work by removing thrombin. (1) fibrin fibers adsorb thrombin (2) antithrombin III (an alpha-globulin, produced in liver and endothelial cells) combine with unadsorbed thrombin and then inactive it.

Anticoagulative factors 3. Heparin. (1) It combines with antithrombin III, then the effectiveness of antithrombin III in removing thrombin increases by a hundredfold to a thousandfold. (2) The complex also removes Xa, XIa, IXa and FXIIa.

Heparin forms a highaffinity complex with antithrombin (AT-H). The formation of ATH complex greatly increases the rate of inhibition of two principle procoagulant proteases, factor Xa and thrombin (FII).

Anticoagulative factors 3. Heparin. (3) Mainly formed in basophilic mast cells in the pericapillary connective tissue and basophilic cells of the blood. (4) Its concentration in the blood is normally low. (5) Widely used as a pharmacological agent in medical practice.

Anticoagulative factors 4. Coumarins

Competitive inhibitors of vitamin K in the of prothrombin 1,3-indanedions biosynthesis  

5.

Tissue factor pathway inhibitor (TFPI, lipoprotein-associated coagulation inhibitor ） 

TFPI in vivo is thought to be synthesized mainly by endothelial cell.



TFPI inhibits the activation of the extrinsic coagulation cascade through its ability to inhibit factor Xa and combine with FVIIa-TF complex.

TF

VII

Ca2+

TF—VIIa—TFPI—Xa Complex of inhibitor

Ca2+ (2) Ca2+

TF—VIIa

TF —Xa

IXa

IX

(1)

X

Xa II

Catalysis

TFPI IIa

Convert

Clot retraction---serum Serum: 



Definition Within a few minutes after a clot is formed, it begins to contract and usually expresses most of the fluid from the clot within 20 to 60 minutes. Difference from plasma: Serum have no fibrinogen and most of other clotting factors.

Fibrinolysis Breakdown of Blood Clots

Fibrinolysis 

Fibrinolysis  Fibrinolysis leads to the breakdown of fibrin clots (blood clots) and is caused by the action of several enzymes  Whenever

fibrinolysin (plasmin) is formed in a blood clot, it can cause lysis of clot and also destruction of many clotting factors, thereby causing hypocoagulability of the blood.

Lysis of blood clots-Plasmin 

Plasminogen (profibrinolysin) mainly formed in liver



Plasminogen can lose one peptide and then convert into plasmin.



Plasmin (fibrinolysin) can digest fibrin fibers, fibrinogen, FV, FVIII, prothrombin and FXII.

Activation of Plasminogen to Form Plasmin 

Activators: Tissue plasminogen activator (t-PA), Urine plasminogen activator (u-PA)



Inhibitors: Plasminogen activator inhibitor type-1 (PAI-1), α 2-antiplasmin

Kallikrein

tPA

uPA

(Endotheli (kidney) um) PAI-1

Plasminogen

(Endotheliu m)

α 2-antiplasmin (liver)

Fibrin (or fibrinogen) Catalysis;

Convert;

FXIIa

Urokinase

Plasmin Fibrin degradation products Inhibit.

In normal situation, fibrinolysis retains at a certain degree and area to keep the balance of Coagulation and Fibrinolysis.









In normal situation, PAI-I is about 10-fold amount of t-PA. So the blood keeps in a hypo-fibrinolysis state. When fibrin forms, endothelium secrete more t-PA, and fibrin has a higher affinity with t-PA and plasminogen. t-PA – fibrin – plasminogen escape the PAI-I inactivation effect on t-PA and help t-PA to activate plasminogen. Plasmin can bind with fibrin to escape α 2-antiplasmin inactivation effect.

Functions of plasmin system To remove minute clots from millions of tiny peripheral vessels to avoid occlusion.

Section 4 Blood Groups Transfusion

Antigenicity causes immune reactions of blood When blood transfusion were first attempted, the transfusions were successful only in some instances.  Failure: agglutination and hemolysis. 

agglutination 

The clumping together of red cells in blood as a result of antibodies attaching to antigens on the surface of the cells. 

Antigens 







Proteins that provide the specific signature or identity to blood or other tissue cells.  When alien antigens are introduced into the body, they stimulate the production and mobilization of antibodies.  Antigens are found on the surface of blood and other tissue cells as well as bacteria and viruses. In blood transfusion failure, the most important antigen is some proteins on the donor’s red cell membrane.

Antibodies  

  

Proteins produced by the body to identify and neutralize or destroy alien antigens.  Antibodies are involved in the rejection of mismatched blood transfusions and organ transplants.  They are also responsible for recognizing and eliminating bacteria and viruses.  Antibodies provide a major defense for our bodies against invasion by alien organisms. In blood transfusion failure, the most important antibody is some proteins in the recipient’s plasma.

Multiplicity of antigens in the blood cells. At least 30 commonly occurring antigens and hundreds of other rare antigens have been found in human blood.  The most important: ABO system and Rh system. 

Discoverer of ABO system Karl Landsteiner discovered ABO blood type in 1900 and 1901.  In 1930, he received the Nobel Prize for this discovery. 

Karl Landsteiner (1868-1943)

ABO blood type 

There are four types: A, B, AB, and O decided by the antigens (Antigen A/B) on RBC membrane.



There are two antigens and two antibodies that are mostly responsible for the ABO types.

Antigen and Antibody in ABO Blood Type ABO Antigen Antigen Antibody Antibody Blood  A    Type B  anti-A anti-B

A

yes

no

no

yes

B

no

yes

yes

no

O

no

no

yes

yes

AB

yes

yes

no

no  

Genetic Inheritance Patterns 

ABO blood types are inherited through genes on chromosome 9



Do not change as a result of environmental influences during life.



An individual's ABO type is determined by the inheritance of 1 of 3 alleles (A, B, or O) from each parent. alleles: alternate forms or varieties of a gene which is responsible for hereditary characteristics. . 

Genotype AA Phenotype A

AO A

BB B

BO B

AB AB

OO O

 There must be two alleles of A, B and O to form a person’s Genotype in blood type.  Both A and B alleles are dominant over O.

Parent Alleles           

A

B

O

A

AA (A)

AB (AB)

AO (A)

B

AB (AB)

BB (B)

BO (B)

O

AO (A)

BO (B)

OO (O)

The possible ABO alleles for one parent are in the top row and the alleles of the other are in the left column. Offspring genotypes are shown in white. Phenotypes are red.

Titer of the agglutinins at different ages. 





Immediately after birth, antibody anti-A and anti-B in plasma are almost zero. 2 to 8 months, infants begin to produce the certain antibody. A maximum titer is usually at 8 to 10 years of age.



The antibody (agglutinins) are IgM (most, spontaneous developed antibody) and IgG (little, immune antibody) immunoglobulin molecules.



Small amounts of group A and B antigens enter the body in food, in bacteria, and in other ways.

Unagglutinated blood smear

Agglutinated blood

Sometimes when the blood of two people is mixed together, it clumps or forms visible islands in the liquid plasma--the red cells become attached to one another.   This is agglutination.

Antibodies seeking specific antigens

Antibodies agglutinating red cells

Agglutination process in transfusion reactions 

IgG (2 binding sites) and IgM (10 binding sites) bind with antigen on RBC membrane.



RBC bound together and clump.



RBC clumps plug small blood vesssels.



Agglutinated cells destroyed (physical distortion or attack by phagocytic white cells) and releasing hemoglobin (hemolysis).





Acute Hemolysis Occurs in some Transfusion Reactions

Antibodies activate the complement system, which releases proteolytic enzymes that rupture the cell membranes. Acute hemolysis is far less common than delayed hemolysis which follows agglutination.

Anti B

Anti A Anti-A-B (Serum) ABO Blood Typing B

A

AB

O

Differences between ABO system and Rh system Contact history

Antigen Blood type

ABO Agglutinins develop spontaneously.

Rh Must be massively exposed to antigens.

A, B A, B, O, AB

C, c, D, d, E, e Positive (have D) Negative (have no D)

Antibody IgM (most, can not go through

IgG (can go through placenta)

Rh immune response 





Formation of Anti-Rh Agglutinins. After being exposed to antigen, anti-Rh agglutinins develop slowly, 2 to 4 months to get the maximum concentration of agglutinins. If an Rh-negative person (never exposed to Rh-positive blood) take transfusion of Rhpositive blood, he will have a delayed mild transfusion reaction. Repeatedly exposition can make transfusion reaction very severe.

Hemolytic disease of the Newborn 



In the case that Mother is Rhnegative and baby is Rh-positive. An Rh-negative mother having her first Rh-positive child usually does not develop sufficient anti-Rh agglutinins to cause any harm.

The rule of Blood Transfusion  



Blood typing. Avoid mismatch. ABO type match and Rh type match (especially in procreation-age woman and patients needing repeated transfusions). Cross-match test 1. 2.



Main test: Donor’s RBC + Recipient’s serum Subordination test: Donor’s serum + Recipient’s RBC

Advances: transfusion of blood components

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