277
lthough the lungs provide the means for gas
exchange between the external and internal envi-
ronments, it is the hemoglobin in the red blood cells that
transports oxygen to the tissues. The red blood cells also
function as carriers of carbon dioxide and participate in
acid–base balance. The function of the red blood cells,
in terms of oxygen transport, is discussed in Chapter 21,
and acid–base balance is discussed in Chapter 8. This
chapter focuses on the red blood cell, anemia, polycy-
themia, and age-related changes in the red blood cells.
The Red Blood Cell
The erythrocytes or mature red blood cells are the
most common type of blood cell, being 500 to 1000
times more numerous than other blood cells. The
erythrocyte is a nonnucleated, thin, biconcave disk
(Fig. 13-1). This unique shape contributes in two ways
to the oxygen transport function of the erythrocyte.
The biconcave shape provides a larger surface area
for oxygen diffusion than would a spherical cell of
the same volume, and the thinness of the cell mem-
brane enables oxygen to diffuse rapidly between the
exterior and the interior of the cell
1–3
(Fig. 13-2A).
Another structural feature that facilitates the transport
function of the red blood cell is the flexibility of its
membrane. The biconcave shape and flexibility of the
red cell membrane are maintained by a complex net-
work of fibrous proteins, especially one called
spectrin
(Fig. 13-3). Spectrin forms an attachment with another
protein, called
ankyrin,
that resides on the inner sur-
face of the membrane and is anchored to an inte-
gral protein that spans the membrane.
2
This unique
arrangement of proteins imparts elasticity and stability
to the red blood cell membrane and allows it to deform
easily as it moves through narrow spaces in the vascu-
lar network.
The function of the red blood cell, facilitated by the
hemoglobin molecule, is to transport oxygen to the tis-
sues. Because oxygen is poorly soluble in plasma, about
95% to 98% is carried bound to hemoglobin. The hemo-
globin molecule is composed of two pairs of structurally
different alpha (
α
) and beta (
β
) polypeptide chains (see
Fig. 13-2B). Each of the four polypeptide chains consists
A
Disorders of Red
Blood Cells
13
C h a p t e r
The Red Blood Cell
Hemoglobin Synthesis
Red Cell Production
Red Cell Life Span and Destruction
Laboratory Tests
Anemia
Blood Loss Anemia
Hemolytic Anemias
Inherited Disorders of the Red Cell Membrane
Sickle Cell Disease
Thalassemias
Inherited Enzyme Defects
Acquired Hemolytic Anemias
Anemias of Deficient Red Cell Production
Iron-Deficiency Anemia
Megaloblastic Anemias
Aplastic Anemia
Anemia of Chronic Disease
Polycythemia
Primary Polycythemia
Secondary Polycythemia
Age-Related Changes in Red Blood Cells
Red Cell Changes in the Neonate
Hyperbilirubinemia in the Neonate
Hemolytic Disease of the Newborn
Red Cell Changes in the Elderly
