A normal WBC count (part of a CBC) is 5,000 to
10,000 per L. Notice that this number is quite small
compared to a normal RBC count. Many of our
WBCs are not circulating within blood vessels but are
carrying out their functions in tissue fluid or in lym-
phatic tissue.
Classification
The five kinds of white blood cells, all produced in the
red bone marrow (and some lymphocytes in lymphatic
tissue), may be classified in two groups: granular and
agranular. The granular leukocytes are the neu-
trophils, eosinophils, and basophils, which usually
have nuclei in two or more lobes or segments, and
have distinctly colored granules when stained.
Neutrophils have light blue granules, eosinophils have
red granules, and basophils have dark blue granules.
The agranular leukocytes are lymphocytes and
monocytes, which have nuclei in one piece.
Monocytes are usually quite a bit larger than lympho-
cytes. A differential WBC count(part of a CBC) is
the percentage of each kind of leukocyte. Normal
ranges are listed in Table 11–2, along with other nor-
mal values of a CBC.
Functions
White blood cells all contribute to the same general
function, which is to protect the body from infectious
disease and to provide immunityto certain diseases.
Each kind of leukocyte makes a contribution to this
very important aspect of homeostasis.
Neutrophils and monocytes are capable of the
phagocytosisof pathogens. Neutrophils are the more
abundant phagocytes, but the monocytes are the more
efficient phagocytes, because they differentiate into
macrophages, which also phagocytize dead or dam-
aged tissue at the site of any injury, helping to make
tissue repair possible. During an infection, neutrophils
are produced more rapidly, and the immature forms,
called band cells (see Fig. 11–2), may appear in
greater numbers in peripheral circulation (band cells
are usually less than 10% of the total neutrophils).
The term “band” refers to the nucleus that has not yet
become segmented, and may look somewhat like a
dumbbell.
Eosinophils are believed to detoxify foreign
proteins and will phagocytize anything labeled with
antibodies. This is especially important in allergic
reactions and parasitic infections such as trichinosis (a
worm parasite). Basophils contain granules of heparin
and histamine. Heparinis an anticoagulant that helps
prevent abnormal clotting within blood vessels.
Histamine, you may recall, is released as part of the
inflammation process, and it makes capillaries more
permeable, allowing tissue fluid, proteins, and white
blood cells to accumulate in the damaged area.
There are two major kinds of lymphocytes, T cells
and B cells, and a less numerous third kind called nat-
ural killer cells. For now we will say that T cells(or T
lymphocytes) help recognize foreign antigens and may
directly destroy some foreign antigens. B cells(or B
lymphocytes) become plasma cells that produce anti-
bodies to foreign antigens. Both T cells and B cells
provide memory for immunity. Natural killer cells
(NK cells) destroy foreign cells by chemically ruptur-
ing their membranes. These functions of lymphocytes
are discussed in the context of the mechanisms of
immunity in Chapter 14.
As mentioned earlier, leukocytes function in tissue
fluid as well as in the blood. Many WBCs are capable
of self-locomotion (ameboid movement) and are able
to squeeze between the cells of capillary walls and out
into tissue spaces. Macrophages provide a good exam-
ple of the dual locations of leukocytes. Some
macrophages are “fixed,” that is, stationary in organs
such as the liver, spleen, and red bone marrow (part of
the tissue macrophage or RE system—the same262 Blood
Table 11–2 COMPLETE BLOOD COUNTMeasurement Normal Range*
Red blood cells
Hemoglobin
Hematocrit
Reticulocytes
White blood cells (total)
Neutrophils
Eosinophils
Basophils
Lymphocytes
Monocytes
Platelets*The values on hospital lab slips may vary somewhat but
will be very similar to the normal ranges given here.- 4.5–6.0 million/L
- 12–18 grams/100 mL
- 38%–48%
- 0%–1.5%
- 5000–10,000/L
- 55%–70%
- 1%–3%
- 0.5%–1%
- 20%–35%
- 3%–8%
- 150,000–300,000/L