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

Blood Clotting and Transfusion

Objectives

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

Content

• 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

Fibrinolysis

• 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

Summary

• 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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