Blood

1.0Blood Group

The blood of all human appears similar but yet differ in certain aspects.

ABO system and Rh factors are taken into consideration.

ABO System

A, B, O system discovered by Karl Landsteiner.

The type of blood group depends on the type of surface antigen or Agglutinogen (Chemicals that can induce immune response), which are two types A & B. These antigens are present in the red blood cell membrane.

Two types of antibodies or Agglutinin (Proteins produced in response to antigen)- anti-A, anti-B are also found in the plasma in the blood.

There are four types of blood groups : A, B, AB and O.

The blood of a donor has to be carefully matched with the blood of a recipient before any blood transfusion to avoid severe problems of clumping (destruction of RBC).

During blood transfusion, the antibodies of receiver attack on antigens of donor if these are same. This may cause severe complications and death of the receiver.

Example

(i) Antigen A + anti-A = death of person due to clumping of RBCs.

(ii) Antigen B + anti-B = death of person due to clumping of RBCs.

Blood groups and Donor Compatibility Table

• It is evident from the table that group ‘O’ blood can be donated to persons with any other blood group and hence ‘O’ group individuals are called ‘universal donors’. 
• Persons with ‘AB’ group can accept blood from persons with AB as well as the other groups of blood, Therefore, such persons are called ‘universal recipients’.

Rh Factor

• Discovered by Landsteiner & Weiner in Rhesus monkey.
• Rh antigen was also found on the surface of RBC of human (Nearly 80%). Such individuals are called (Rh+ve).
• On the basis of this antigen blood group can be positive (+) or negative (–).
• Rh antibodies are naturally absent.

• If receiver is positive and donor is negative, then transfusion is always safe.
• If receiver is negative and donor is positive, then only first transfusion is safe.
• Therefore Blood group O^–  is universal donor and AB⁺ is a universal recipient (Acceptor).

Rh Factor Incompatibility

Rh antigen is due to dominant gene. An Rh-ve person if exposed to Rh+ve blood, will form specific antibodies against the Rh antigen.

2.0Erythroblastosis Foetalis

• If mother is Rh^– & father is Rh⁺ then offspring will be Rh⁺. 
• In this case 1^st pregnancy is completely successful due to the separation of blood through placenta, but at the time 1^st delivery Rh antibody is formed in mother's blood due to breaking of blood vessels at the time of delivery.
• Now in subsequent delivery Rh antibodies from the mother (Rh –ve) can leak into the blood of the foetus (Rh +ve) and destroy the foetal RBCs.
• This could be fatal to the foetus or could cause severe anaemia and jaundice to the baby. So in next pregnancy death of foetus will occur in the earlier stage due to agglutination of blood called erythroblastosis foetalis/HDN (Hemolytic disease of newborn).

Treatment - To make the second pregnancy safe, medicines like RhoGAM, Anti-D etc. are administered to the mother immediately after the delivery of first child.

3.0Blood Clotting (Coagulation of Blood)

• Whenever we get hurt by a sharp object bleeding occurs and blood oozes out also called exudation of blood.
• Blood flows from cuts or wounds but after sometimes it stops automatically, it is called clotting of blood.
• Clot or coagulam formed mainly of a network of threads called fibrins in which dead and damaged formed elements of blood are trapped. 
• Fibrins are formed by the conversion of inactive fibrinogens in the plasma by the enzyme thrombin. 
• Thrombins, in turn are formed from another inactive substance present in the plasma called prothrombin. 
• An enzyme complex, thrombokinase, is required for the above reaction. 
• This complex is formed by a series of linked enzymic reactions (cascade process) involving a number of factors present in the plasma in an inactive state. 
• An injury or a trauma stimulates the platelets in the blood to release certain factors which activate the mechanism of coagulation. 
• Certain factors released by the tissues at the site of injury also can initiate coagulation. 
• Calcium ions play a very important role in clotting.

(Its network + dead damaged formed elements of blood are trapped in it = Clot/coagulam (Reddish brown scum)

Blood– Corpuscles = Plasma; Plasma– fibrinogen and large proteins = Serum

4.0Blood Vessels

In closed type of blood vascular system, blood vessels are of 3 types: 

(1) Arteries (2) Veins (3) Capillaries

Artery carries oxygenated blood from heart to the different organs of the body.

Veins carry deoxygenated blood from body organs to the heart. 

Capillaries are present in the organs, and these are the vessels through which exchange of materials takes place between blood and tissues.

Anatomy of arteries and veins: Normally three layers are found in the walls of blood vessels:

(i) Tunica external: It is the outermost layer. It is formed of loose connective tissue in which many collagen fibres, elastin fibres and longitudinal muscles are found.

(ii) Tunica media: It is a thick layer of circular non-striated muscles and a network of elastin fibres.

(iii) Tunica internal/intimal: This layer is made up of squamous epithelium, it is also known as endothelium.

One more layer is present in the wall of bigger arteries, that is known as elastic membrane. This is found in between the tunica media and tunica internal layers.

These all layers are well developed in the walls of arteries as compared to the walls of veins.

Walls of arteries are thick and more muscular and these walls are elastic and non-collapsable.

The walls of veins are thin, less muscular, non-elastic and collapsable.

In the walls of blood capillaries, only endothelium layer is found. It is made up of simple squamous epithelium. These blood capillaries join the arteries with the veins.

Main differences in Arteries, Veins and Capillaries