Module 8 Intro

Module 8—Circulation, Immunity, and Excretion

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The Rh System

In addition to the ABO blood-typing system, the presence or absence of the Rh factor (antigen) determines if an individual is Rh positive or Rh negative. An Rh+ individual has the Rh antigen on his or her blood cells, while an Rh- individual will lack Rh antigens. The Rh system was named after the rhesus monkey, since these monkeys were used to research blood typing.

A problem can arise if Rh- individuals are exposed to Rh+ blood. This typically happens when a pregnant woman (Rh-) gives birth to a baby who carries the Rh antigen because blood often mixes during childbirth. Once the mother is exposed to Rh+ blood, her body will identify this blood as a foreign substance and create Rh+ antibodies.

In possible subsequent pregnancies, where a baby is again Rh+, the mother’s antibodies may cross the placenta and endanger the child. A condition referred to as hemolytic disease of the newborn (HDN) can occur.

The Rh+ antibodies from the mother will begin destroying the baby’s blood cells and can lead to brain damage, deafness, and death. A series of diagrams on page 297 of the textbook illustrates and explains the mechanism of Rh incompatibility.

Self-Check

Use the following information to answer the next two questions.

ABO Blood Type System and The RH System

SC 2. Which individual in the chart above would have Type O negative blood?

1. Individual A
2. Individual B
3. Individual C
4. Individual D

SC 3.  All of the individuals identified in the chart above are females, all had previous pregnancies with men who are Rh+, and all become pregnant a second time. Which individuals in the chart would have to be concerned about hemolytic disease of the newborn (HDN)?

1. Individuals A and C
2. Individuals A and B
3. Individuals B and D
4. Individuals C and D

Biology 20 © 2008 Alberta Education