652
UNIT 4
Maintenance of the Body
17
before
birth to provide the fetus with more erythrocytes for oxy-
gen transport. Additionally, one or two
exchange transfusions
(see Related Clinical Terms, p. 657) are done aFer birth. ±e
baby’s Rh
1
blood is removed, and Rh
2
blood is infused. Within
six weeks, the transfused Rh
2
erythrocytes have been broken
down and replaced with the baby’s own Rh
1
cells.
Transfusion Reactions:
Agglutination and Hemolysis
When mismatched blood is infused, a
transfusion reaction
oc-
curs in which the recipient’s plasma agglutinins attack the do-
nor’s red blood cells. (Note that the donor’s plasma antibodies
may also agglutinate the recipient’s RBCs, but these antibodies
are so diluted in the recipient’s circulation that this does not
usually present a problem.)
±e initial event, agglutination of the foreign red blood cells,
clogs small blood vessels throughout the body. During the next
few hours, the clumped red blood cells begin to rupture or are
destroyed by phagocytes, and their hemoglobin is released into
the bloodstream. When the transfusion reaction is exception-
ally severe, the RBCs are lysed almost immediately.
±ese events lead to two easily recognized problems: (1)
±e transfused blood cells cannot transport oxygen, and (2)
the clumped red blood cells in small vessels hinder blood flow
to tissues beyond those points. Less apparent, but more devas-
tating, is the consequence of hemoglobin that escapes into the
bloodstream. Circulating hemoglobin passes freely into the kid-
ney tubules, causing cell death and renal shutdown. If shutdown
is complete (acute renal failure), the recipient may die.
Unlike the ABO system antibodies, anti-Rh antibodies do
not spontaneously form in the blood of Rh
2
(Rh negative) in-
dividuals. However, if an Rh
2
person receives Rh
1
blood, the
immune system becomes sensitized and begins producing anti-
Rh antibodies against the foreign antigen soon aFer the transfu-
sion. Hemolysis does not occur aFer the first such transfusion
because it takes time for the body to react and start making anti-
bodies. But the second time, and every time thereaFer, a typical
transfusion reaction occurs in which the recipient’s antibodies
attack and rupture the donor RBCs.
Homeostatic Imbalance
17.3
An important problem related to the Rh factor occurs in pregnant
Rh
2
women who are carrying Rh
1
babies. ±e first such pregnancy
usually results in the delivery of a healthy baby. But, when bleeding
occurs as the placenta detaches from the uterus, the mother may
be sensitized by her baby’s Rh
1
antigens that pass into her blood-
stream. If so, she will form anti-Rh antibodies unless treated with
RhoGAM before or shortly aFer she has given birth. (±e same
precautions are taken in women who have miscarried or aborted
the fetus.) RhoGAM is a serum containing anti-Rh agglutinins.
By agglutinating the Rh factor, it blocks the mother’s immune re-
sponse and prevents her sensitization.
If the mother is not treated and becomes pregnant again with
an Rh
1
baby, her antibodies will cross through the placenta
and destroy the baby’s RBCs, producing a condition known as
hemolytic disease of the newborn
, or
erythroblastosis fetalis
.
±e baby becomes anemic and hypoxic. In severe cases, brain
damage and even death may result unless transfusions are done
Table 17.4
ABO Blood Groups
FREQUENCY (% OF U.S. POPULATION)
BLOOD
GROUP
RBC
ANTIGENS
(AGGLUTINOGENS)
ILLUSTRATION
PLASMA
ANTIBODIES
(AGGLUTININS)
BLOOD
THAT CAN
BE RECEIVED
WHITE
BLACK
ASIAN
NATIVE
AMERICAN
AB
A
B
None
A, B, AB, O
“Universal
recipient”
4
4
5
,
1
B
B
Anti-A (a)
B, O
11
20
27
4
A
A
Anti-B (b)
A, O
40
27
28
16
O
None
Anti-A (a)
Anti-B (b)
O “Universal
donor”
45
49
40
79
A
B
B
Anti-A
Anti-B
A
Anti-A
Anti-B
previous page 686 Human Anatomy and Physiology (9th ed ) 2012 read online next page 688 Human Anatomy and Physiology (9th ed ) 2012 read online Home Toggle text on/off