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Some stem cells will differentiate into proeryth-
roblasts, which will eventually lose their nuclei and become
mature RBCs. Some stem cells will become myeloblasts.
These cells will develop into progranulo-cytes. Some of
these cells will develop into basophilic myelocytes and will
mature into basophils, others will develop into eosinophilic
myelocytes and will mature into eosinophils,- while still
others will develop into neu-trophilic myelocytes and will
mature into neutrophils. Other stem cells will become
lymphoblasts and will mature into lymphocytes; some stem
cells will become monoblasts and will mature into
monocytes. Finally, some stem cells will become
megakaryoblasts and will undergo multipolar mitosis of the
nucleus to mature into blood platelets. All stages of blood
cell development will be found in red bone marrow tissue.
Blood Cell Anatomy
and Functions
Erythrocytes appear as biconcave disks with edges that are
thicker than the center of the cell, looking somewhat
doughnut-shaped. They do not have a nucleus and are
simple in structure. They are composed of a network of
protein called stroma, cytoplasm, some lipid sub-stances
including cholesterol, and a red pigment called
hemoglobin (hee-moh-GLOH-bin). Hemoglobin con-
stitutes 33% of the cell’s volume. Erythrocytes contain
about 280 million molecules of hemoglobin per eryth-
rocyte. Because they have lost their nuclei, they do not
divide. They function for approximately 120 days.
The primary function of erythrocytes is to combine
with oxygen in the lungs and to transport it to the various
tissues of the body. It then combines with carbon dioxide in
tissues and transports it to the lungs for expulsion from the
body. The pigment hemoglobin allows this to happen.
Hemoglobin is made of a protein called globin (GLOH-
bin) and a pigment called heme (HEEM). The pigment
heme contains four iron atoms. The iron atoms of heme
combine with the oxygen in the lungs. In the tissues of the
body, the oxygen is released and the protein globin now
combines with the carbon dioxide from the intersti-tial
fluids and carries it to the lungs where it is released.
Hemoglobin that is carrying oxygen is bright red in color,
whereas hemoglobin not carrying oxygen is a darker red in
color. A healthy man has 5.4 million RBCs/mm^3 of blood
and a healthy woman has 4.8 -million RBCs/mm^3 of blood.
Due to menstruation and loss of blood, some women need
more iron in their diet for the most efficient transport of
oxygen by their blood.
Chapter 13Leukocytes have nuclei and no pigment. Their general-
function is to combat inflammation and infec-tion. They are
called white blood cells because they lack pigmentation.
They are larger in size than RBCs and are carried by the
blood to various tissues in the body. They have the ability
to leave the blood and move into tissues by ameboid
movement, sending out a cytoplas-mic extension that
attaches to an object while the rest of the cell’s contents
then flow into that extension. In this manner, the leukocytes
attack invading microorganisms and clean up cellular
debris by consuming this material by phagocytosis-
(fag-oh-sigh-TOH-sis), which means eating- cells.When stained with Wright’s stain, the cytoplasm of
leukocytes shows the presence or absence of gran-ules.
Therefore, leukocytes are divided into the -granular
leukocytes and the agranular (a means without) or
nongranular leukocytes. The three types of granular leu-
kocytes are neutrophils, basophils, and eosinophils. The
two types of nongranular leukocytes are monocytes and
lymphocytes.Neutrophils are the most common of leukocytes. They
are the most active WBCs in response to tissue- de-
struction by bacteria. They stay in the blood for about 12
hours and then move into tissues where they phagocy-tize
foreign substances and secrete the enzyme -lysozyme
(LYE-soh-zyme), which destroys certain bacteria. When
pus accumulates at an infection area, it consists of cell
debris, fluid, and dead neutrophils.
Monocytes are also phagocytotic. They phagocytize
bacteria and any dead cells or cellular debris. They are the
largest leukocytes. After they leave the blood and enter
tissues, they increase in size and are called macro-
phages (MACK-roh-fay-jeez).
Eosinophils combat irritants, such as pollen or cat hair,
that cause allergies. They produce antihistamines. Their
chemical secretions also attack some worm para-sites in the
body.
Basophils are also involved in allergic reactions. They
release heparin (an anticoagulant), histamine (an
inflammatory substance), and serotonin (a vasocon-strictor)
into tissues.
Lymphocytes are involved in the production of anti-
bodies and play a crucial role in the body’s immune re-
sponse. They are the smallest of the leukocytes. There are
two types of lymphocytes: the B lymphocytes and the T
lymphocytes, which are discussed further in Chapter- 15.
They are involved in controlling cancer cells, destroying
microorganisms and parasites, and rejecting foreign tis-sue
implants.