Page 129 - 84 human physiolofy part-1

Blood Physiology

controlled by a single gene with three alleles: i, IA, and IB. The gene encodes an enzyme that modifies
the carbohydrate content of the red blood cell antigens.

IA gives type A,
IB gives type B,
i give types O

IA and IB are dominant over i, so ii people have type O, IAIA or IAi have A, and IBIB or IBi have
type B. IAIB people have both phenotypes because A and B are codominant, which means that type A
and B parents can have an AB child. Thus, it is extremely unlikely for a type AB parent to have a type
O child (it is not, however, direct proof of illegitimacy): the cis-AB phenotype has a single enzyme that
creates both A and B antigens. The resulting red blood cells do not usually express A or B antigen at
the same level that would be expected on common group A or B red blood cells, which can help solve
the problem of an apparently genetically impossible blood group.

Rh Factor

Many people have the Rh Factor on the red blood cell. Rh carriers do not have the antibodies for
the Rh Factor, but can make them if exposed to Rh. Most commonly Rh is seen when anti-Rh
antibodies cross from the mothers placenta into the child before birth. The Rh Factor enters the child
destroying the child's red blood cells. This is called Hemolytic Disease.

Compatibility in Blood Transfusions

Blood transfusions between donor and recipient of incompatible blood types can cause severe
acute immunological reactions, hemolysis (RBC destruction), renal failure, shock, and sometimes
death. Antibodies can be highly active and can attack RBCs and bind components of the complement
system to cause massive hemolysis of the transfused blood.

A patient should ideally receive their own blood or type-specific blood products to minimize the
chance of a transfusion reaction. If time allows, the risk will further be reduced by cross-matching
blood, in addition to blood typing both recipient and donor. Cross-matching involves mixing a sample
of the recipient's blood with a sample of the donor's blood and checking to see if the mixture
agglutinates, or forms clumps. Blood bank technicians usually check for agglutination with a
microscope, and if it occurs, that particular donor's blood cannot be transfused to that particular
recipient. Blood transfusion is a potentially risky medical procedure and it is vital that all blood
specimens are correctly identified, so in cross-matching labeling is standardized using a barcode system
known as ISBT 128.

Hemolytic Disease of the Newborn

Often a pregnant woman carries a fetus with a different blood type to herself, and sometimes the
mother forms antibodies against the red blood cells of the fetus, leading to low fetal blood counts, a
condition known as hemolytic disease of the newborn.

Hemolytic disease of the newborn, (also known as HDN) is an alloimmune condition that develops
in a fetus when the IgG antibodies produced by the mother and passing through the placenta include

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