Blood Clotting and Transfusion - Human Anatomy and Physiology B. Pharma 1st Semester

Blood Clotting and Transfusion


At the end of this lecture, student will be able to

• Describe blood clotting

• Explain the ABO and Rh blood groups

• Outline the concept of blood transfusion

• Explain ABO blood group interactions

• Explain Erythroblastosis Foetalis


• Blood clotting

• Concept of blood grouping

• Blood grouping interactions

Blood Clotting (Coagulation)

Blood Clotting

• Extrinsic pathway and the intrinsic pathway lead to the formation of prothrombinase

• Prothrombinase converts prothrombin (a plasma protein formed by the liver) into the enzyme thrombin

• Thrombin converts soluble fibrinogen (another plasma protein formed by the liver) into insoluble fibrin 

• Fibrin forms the threads of the clot

Role of Clotting Factors

Clotting Factors


• Dissolution of clot

• Mechanism

– Plasminogen (a plasma protein) is activated by many factors & becomes Plasmin

– Plasmin then breaks down fibrin meshwork

– Phagocytic WBCs remove products of clot dissolution

Haemostatic Mechanism Overview

Thrombus and Embolus

• Thrombus - clot formed in an intact vessel, possibly due to:

 Roughened vessel walls

 Slow-moving blood (e.g. in varicose veins)

Blood Groups

Antigens (Agglutinogens)

• The surfaces of RBC contain a genetically determined assortment of antigens

• Composed of glycoproteins and glycolipids

• 24 blood groups

• ABO and Rh

• The Lewis, Kell, Kidd & Duffy systems

Significance of Antigen

• Based on the presence or absence of various antigens, blood is categorized into different blood group

• A, B, AB and O

Antigens and Antibodies of ABO Blood Types

ABO Blood Group Interactions

Concept of Blood Transfusion

Rh Blood Group

• Rh - Antigen was discovered in the blood of the Rhesus monkey

• Rh antigens present - Rh positive and vice versa

• Normally blood plasma dose not cantain anti-Rh antibodies

• To a Rh- person if Rh+ blood is given - Immune system starts to make anti-Rh antibodies that will remain in the blood

• A second transfusion of Rh+ blood is given later

• The previously formed anti Rh antibodies will cause agglutination and hemolysis of the RBCs in the donated blood

Blood Grouping

Erythroblastosis Foetalis


• Extrinsic pathway and the intrinsic pathway lead to the formation of prothrombinase in blood clotting

• The  ABO  blood  grouping    Based  on  antigen  (A  or  B)  and antibody ( A or B) type

• Rh blood type - Based on another surface antigen called either Rh or D

• Erythroblastosis Foetalis: Rh incompatibility between mother and foetus

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