5–131 The thymus secretes a hormone called thymosin, which stimulates the red
bone marrow to produce T lymph/o/cytes, or T cells. T cells are important in the
immune process. They originate in the bone marrow but migrate and mature in the
thymus. Upon maturation, T cells enter the blood and circulate throughout the
body, providing a mechanism of defense against disease because the cells attack and
destroy foreign or abnormal cells.
Specific lymph/o/cytes that attack foreign agents, such as viruses, are known as
T lympho/cytes or _______________.5–132 Some T cells are called killer T cells or cytotoxic T lymphocytes (CTLs)
because they secrete immun/o/logic/ally essential chemical compounds that destroy
foreign cells. These killer cells are so named because they are capable of destroying
specific cells. The killer cells also play a significant role in the body’s resistance to
proliferation of cancer (CA) cells.
Specialized cells that provide surveillance against CA cells are called killer
T lymph/o/cytes or __________ / _____ / __________ / __________
T lymph/o/cytes.
The abbreviation for cancer is __________.5–133 CTLs defend against viral and fung/al infections. They are also responsi-
ble for transplant rejection reactions and for immun/o/logic/al surveillance against
cancer.
The abbreviation CTL stands for __________ / _____ / __________ / __________
_____ ____________________ / _____ / __________.Competency Verification:Check your labeling of Figure 5–10 in Appendix B: Answer Key, page 575.
Frame 5–125to Frame 5–133Lymphatic System • CHAPTER 5 187T cellscyt/o/tox/ic
sī-tō-TŎKS-ĭkCAcyt/o/tox/ic T lymph/
o/cyte
sī-tō-TŎKS-ĭk LĬM-fō-sīt