Body Fluids and Circulation — Bio Zoology STD 11 — Question
Tamilnadu BoardEnglish MediumSTD 11Bio ZoologyBody Fluids and Circulation5 Marks
Question
Explain the role of the Rh factor?
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Answer
Rh factor is a protein (D antigen) present on the surface of the red blood cells in the majority (80\%) of hum. This protein is similar to the protein present in Rhesus monkey, hence the term Rh. Individuals who carry the antigen D on the surface of the red blood cells are Rh+ (Rh-positive) and the individuals who do not carry antigen D, are $Rh ^{-}$(Rh-negative). Rh factor compatibility is also checked before blood transfusion.
When a pregnant woman is $Rh ^{+}$and the foetus is $Rh ^{+}$incompatibility (mismatch) is observed. During the first pregnancy, the Rh antigens of the fetus do not get exposed to the mother's blood as both their blood are separated by the placenta. However, a small amount of the foetal antigen becomes exposed to the mother's blood during the birth of the first child.
The mother's blood starts to synthesize D antibodies. But during subsequent pregnancies, the Rh antibodies from the mother ( $Rh ^{-}$) enters the foetal circulation and destroys the foetal RBCs. This becomes fatal to the foetus because the child suffers from anaemia and jaundice. This condition is called erythroblastosis foetalis. This condition can be avoided by administration of anti D antibodies (Rhocum) to the mother immediately after the first childbirth.
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