2.7 Flashcards
When blood is transfused, it is important that people are given blood of the
Correct blood group
People with sickle-cell anaemia may need to be given a
Blood transfusion
Blood groups are determined by the
Antigens present on the red blood cells -
These antigens are inherited
There are several antigens present in this blood group, but the main one is known as
Antigen D
People who have antigen D on their red blood cells are
Rhesus positive
Antigen D is codes do by the dominant allele,
D
People who do not have antigen D on their red blood cells are
Rhesus negative
People who are rhesus positive may have the genotype
DD or Dd
People who are rhesus negative have the genotype
dd
It is possible for a rhesus negative mother to be pregnant with a rhesus positive baby. The mother’s blood and the baby’s blood do not mix in the placenta. However it is possible for the baby’s blood to come into
Contact with the mother’s blood around the time of childbirth
When mother’s blood and baby’s blood comes into contact, the mother’s immune system will make
Antibodies against the rhesus antigen
If the mother becomes pregnant with a second rhesus positive baby, problems may be more severe. Antibodies pass from the mother’s blood to the baby’s across the
Placenta
The mother’s anti-rhesus antibodies pass across the placenta and attack the baby’s red blood cells. This destroys them and causes severe anaemia. The condition is called
Haemolytic disease of the newborn
Haemolytic disease of the newborn varies in severity in mild forms the baby is born with
anaemia and jaundice
Haemolytic disease of the newborn in severe cases the baby may develop
Respiratory arrest or heart failure
Or even still born
Haemolytic disease of the newborn can be prevented by giving pregnant women who are rhesus negative an
Injection of anti-rhesus globulin and repeating the injection after the birth of a rhesus positive baby.
(Haemolytic disease of the newborn) if the injection is done the mother should be have to have further
Rhesus positive babies without any risk
The best known blood group system is the
ABO system
There are 4 blood groups in this system:
A
B
AB
O
People with group A have:
A antigens on their RBC
Group B=
B antigens on their RBC
Group AB have:
Both kinds of antigen
Group O have:
Neither of these antigens on their RBC
People with different blood groups also have different
Antibodies on their plasma
When a person is given a blood transfusion it is important that the antigens of the donor should be compatible with the antibodies of the
Recipient
If a person is given blood of the wrong blood group, their antibodies clump the donor RBC known as
Agglutination
Agglutination can block
Blood vessels and can be fatal
ABO blood groups are inherited they are determined by a single gene with 3 different alleles. This is an example of inheritance involving
Multiple alleles
Two alleles IA and IB are co dominant while IO is
Recessive
