532
UNIT FOUR
release
histamine,
which promotes infl ammation, and
hepa-
rin,
which inhibits blood clotting, thus increasing blood fl
ow
to injured tissues. Basophils usually account for less than
1% of the leukocytes.
The leukocytes of the agranulocyte group include mono-
cytes and lymphocytes. Monocytes generally arise from red
bone marrow. Lymphocytes are formed in the organs of the
lymphatic system as well as in the red bone marrow (see
chapter 16, p. 628).
Monocytes
(mon
o-sı¯tz) are the largest blood cells, two
to three times greater in diameter than red blood cells. Their
nuclei are spherical, kidney-shaped, oval, or lobed
(f g. 14.13)
.
Monocytes leave the bloodstream and become
macrophages
that phagocytize bacteria, dead cells, and other debris in the
tissues. They usually make up 3% to 9% of the leukocytes in
a blood sample and live for several weeks or even months.
Lymphocytes
(lim
fo-sı¯tz) are usually only slightly
larger than erythrocytes. A typical lymphocyte has a large,
spherical nucleus surrounded by a thin rim of cytoplasm
(f g. 14.14)
. The major types of lymphocytes are
T cells
and
B cells,
both important in
immunity.
T cells directly attack
microorganisms, tumor cells, and transplanted cells (see
chapter 16, p. 630). B cells produce
antibodies
(see chapter 16,
p. 632), which are proteins that attack foreign molecules.
Lymphocytes account for 25% to 33% of the circulating leu-
kocytes. They may live for years.
PRACTICE
16
Which hormones are necessary for the diF
erentiation of white
blood cells from hematopoietic stem cells in red bone marrow?
17
Distinguish between granulocytes and agranulocytes.
18
List ±
ve types of white blood cells, and explain how they diF
er
from one another.
19
Describe the function of each type of white blood cell.
FIGURE 14.12
A basophil has cytoplasmic granules that stain deep
blue (2,000
×
). This type of white blood cell produces heparin, which
prevents inappropriate blood clotting, and histamines, which increase
circulation to injured tissues. Basophils also take part in certain allergic
reactions.
FIGURE 14.10
A neutrophil has a lobed nucleus with two to ±
ve
components (2,000
×
). This blood cell type has abundant lysosomes,
which contain enzymes that break down parts of phagocytized
bacteria.
FIGURE 14.11
An eosinophil has red-staining cytoplasmic granules
(2,000
×
). This type of white blood cell kills certain parasites and helps
to control in²
ammation and allergic reactions.
FIGURE 14.13
A monocyte is the largest of the blood cells (2,000
×
).
It may leave the bloodstream and become a macrophage, which is
a wandering phagocytic cell that destroys damaged red blood cells.
Note the platelet indicated by the arrow.
previous page 562 David Shier Hole's Human Anatomy and Physiology 2010 read online next page 564 David Shier Hole's Human Anatomy and Physiology 2010 read online Home Toggle text on/off