The Circulatory System
Lesson 8, Page 6 of 12

The blood cell type responsible for the transport of oxygen and carbon dioxide is the red blood cell (erythrocytes.)

White Blood Cells

The leukocytes, or white blood cells, are of three types; granulocytes, lymphocytes, and monocytes. All are involved in defending the body against foreign organisms.

There are three types of granulocytes: neutrophils, eosinophils, and basophils, with neutrophils the most abundant. Neutrophils seek out bacteria and phagocytize, or engulf, them.

The lymphocytes' chief function is to migrate into the connective tissue and build antibodies against bacteria and viruses. Leukocytes are almost colorless, considerably larger than red cells, have a nucleus, and are much less numerous; only one or two exist for every 1,000 red cells. The number increases in the presence of infection.

Monocytes, representing only 4 to 8 percent of white cells, attack organisms not destroyed by granulocytes and leukocytes.

The granulocytes, accounting for about 70 percent of all white blood cells, are formed in the bone marrow. The lymphocytes on the other hand are produced primarily by the lymphoid tissues of the body—the spleen and lymph nodes. They are usually smaller than the granulocytes. Monocytes are believed to originate from lymphocytes. Just as the oxygen-carrying function of red cells is necessary for our survival, so are normal numbers of leukocytes, which protect us against infection.

Fighting infection and foreign invaders is one of the primary functions of the ________.

erythrocytes (red blood cells)
leukocytes (white blood cells)
thrombocytes (platelets)
all of the above

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