Page 2 - ln- Ch-18 1

responsible for immune response of the body.

Thrombocytes or platelets are cell fragments produced from megakaryocytes in bone
marrow. 150000-350000 platelets are present in each ml of blood. Platelets are involved in

clotting or coagulation of blood in case of injuries.

Blood Groups - blood of human beings differ in certain aspects although it appear same in
all individuals. Two main types of grouping are ABO and Rh.

ABO grouping is based on presence or absence of two surface antigens RBC, antigen A and
antigen B. The plasma of an individual also contains two antibodies produced in response of

antigens.

• During blood transfusion, blood of donor has to be matched with blood of recipients
to avoid clumping of RBCs.

• Group '0' blood can be donated to any individual with any blood group, so it is called
universal donor.

• Person with 'AB' blood group can receive blood from any person of any group, so it is

called universal recipient.

Rh grouping - Rh antigen (similar to Rhesus monkey) are observed on surface of RBCs of
majority of individuals (about 80%). Such people are called Rh positive (Rh+) and those in

whom this antigen is absent are called Rh negative (Rh-).

• Erythroblastosis foetalis- if father blood is Rh+ and mother blood is Rh:', the foetus

blood is Rh+. During the delivery of first child there is a possibility of exposure of
mother blood with foetus blood to develop antibodies in mother blood. In subsequent

pregnancy the mother's blood can leak into foetus blood and destroy the foetus RBC.

Coagulation of blood (Blood Clotting)

When an injury is caused to a blood vessel bleeding starts which is stopped by a process

called blood clotting. An injury or trauma stimulates the platelets in the blood to release
certain factors that activate the mechanism of coagulation. Calcium play important role in

blood clotting.

Lymph

2/8