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TABLE 22–1 Blood Cells
TYPE OF CELL
MAIN FUNCTIONS
TYPICAL CONCENTRATION
IN HUMAN BLOOD
(CELLS/LITER)
Red blood cells
transport O2 and CO2
5 ¥ 1012
(erythrocytes)
White blood cells
(leucocytes)
Granulocytes
Neutrophils
phagocytose and destroy invading
5 ¥ 109
(polymorphonuclear
bacteria
leucocytes)
Eosinophils
destroy larger parasites and modulate
2 ¥ 108
allergic inflammatory responses
Basophils
release histamine (and in some species
4 ¥ 107
serotonin) in certain immune reactions
Monocytes
become tissue macrophages, which
4 ¥ 108
phagocytose and digest invading
microorganisms and foreign bodies as
well as damaged senescent cells
Lymphocytes
B cells
make antibodies
2 ¥ 109
T cells
kill virus-infected cells and regulate
1 ¥ 109
activities of other leucocytes
Natural killer
kill virus-infected cells and some
1 ¥ 108
(NK) cells
tumor cells
Platelets
initiate blood clotting
3 ¥ 1011
(cell fragments arising
from megakaryocytes
in bone marrow)
Humans contain about 5 liters of blood, accounting for 7% of body weight. Red blood cells
constitute about 45% of this volume and white blood cells about 1%, the rest being the
liquid blood plasma.
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