548
UNIT FOUR
Erythroblastosis fetalis is extremely rare today because obstetricians
carefully track Rh status. An Rh
woman who might carry an Rh
+
fetus
is given an injection of a drug called RhoGAM. This is anti-Rh anti-
bodies, which bind to and shield any Rh
+
fetal cells that might con-
tact the woman’s cells and sensitize her immune system. RhoGAM
must be given within seventy-two hours of possible contact with Rh
+
cells—including giving birth, terminating a pregnancy, miscarrying,
or undergoing amniocentesis (a prenatal test in which a needle is
inserted into the uterus).
newborn. Transfusions with Rh-negative blood are given to
the fetus before birth and to the neonate after birth to avoid
brain damage or possibly death.
Table 14.14
describes a few of the many and diverse
inherited disorders that affect the blood.
PRACTICE
53
What is the Rh blood group?
54
What are two ways that Rh incompatibility can arise?
TABLE
14.14
|
Some Inherited Disorders of Blood
Disorder
Abnormality
Chronic granulomatous disease
Granulocytes cannot produce superoxide, which kills pathogenic bacteria
Erythrocytosis
Reticulocytes have extra EPO receptors, enhancing stamina
Factor V Leiden
Increases risk of abnormal clotting; elevates risk of deep vein thrombosis
Hemophilia (several types)
Lack of speci±
c clotting factor causes bleeding
Hereditary hemochromatosis
Excess absorption of dietary iron into bloodstream deposits iron in various organs
Porphyria variegata
Enzyme de±
ciency excretes porphyrin ring of hemoglobin into urine; metabolic blockage causes sequence of varied symptoms
Sickle cell disease
Abnormal hemoglobin crystallizes under low-oxygen conditions, sickling red blood cells, which block circulation causing
anemia, pain, and other symptoms
Von Willebrand disease
Lack of clotting factor (von Willebrand factor), which stabilizes factor VIII, causes bleeding; less severe than hemophilia
c. The mature form lacks nuclei and other organelles,
but contains enzymes needed for energy-releasing
processes.
3. Red blood cell counts
a. The red blood cell count equals the number of cells
per microliter of blood.
b. The average count may range from approximately
4,000,000 to 6,000,000 cells per microliter.
c. Red blood cell count is related to the oxygen-
carrying capacity of the blood and is used in
diagnosing and evaluating the courses of diseases.
4. Red blood cell production and its control
a. During fetal development, red blood cells form
in the yolk sac, liver, and spleen; after birth, red
blood cells are produced by the red bone marrow.
b. The number of red blood cells remains relatively
stable.
c. A negative feedback mechanism involving
erythropoietin from the kidneys and liver controls
rate of red blood cell production.
(1) Erythropoietin is released in response to low
oxygen levels.
(2) High altitude, loss of blood, or chronic lung
disease can lower oxygen concentration in the
blood.
CHAPTER SUMMARY
14.1
INTRODUCTION (PAGE 523)
Blood is often considered a type of connective tissue in
which cells are suspended in a liquid extracellular matrix.
It transports substances between the body cells and the
external environment and helps maintain a stable internal
environment. Blood volume varies with body size, fl
uid
and electrolyte balance, and adipose tissue content. Blood
can be separated into formed elements (mostly red blood
cells) and liquid portions—plasma.
14.2
BLOOD CELLS (PAGE 524)
1. The origin of blood cells
a. Blood cells develop from hematopoietic stem cells
in red bone marrow.
b. Cells descended from stem cells respond to
hematopoietic growth factors to specialize.
c. Thrombopoietin stimulates megakaryocytes to give
rise to platelets, much as erythropoietin stimulates
formation of red blood cells.
2. Characteristics of red blood cells
a. Red blood cells are biconcave discs with shapes
that provide increased surface area and place their
cell membranes close to internal structures.
b. Red blood cells contain hemoglobin, which
combines loosely with oxygen.
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