White Blood Cells
White blood cells(WBCs) are usually larger than red blood cells. They have a nucleus
but do not have hemoglobin. White blood cells make up less than one percent of the blood’s
volume. Most WBCs are made in the bone marrow, some mature in the lymphatic system.
WBCs defend the body against infection by bacteria, viruses and other pathogens. Each
WBC type has a specific defense job. Three of the most common white blood cells in the
body are listed here.
- Neutrophilscan squeeze through capillary walls and swallow particles such as bacteria
and parasites. - Macrophagescan also swallow and destroy old and dying cells, bacteria, or viruses.
In Figure18.17a macrophage is attacking and swallowing two particles, possibly
pathogens. Macrophages also release chemical messages that cause the number of
WBC to increase. - Lymphocytesfightinfectionsbyvirusesandbacteria. Somelymphocytesattackandkill
cancer cells. Other lymphocytes attack cells that are infected by viruses. Lymphocytes
called B-cells make antibodies. Antibodiesare chemicals that identify pathogens or
other substances as being harmful, or they can destroy the pathogen. To learn more
about the role of WBCs in protecting the body from infection, go to theDiseases and
the Body’s Defenseschapter.
Figure 18.17: A type of WBC, called a macrophage, is attacking and about to swallow two
particles. ( 23 )