ABSTRACT
The endocrine system of the human body is a system of glands and organs that produce, receive, and manipulate many substances including hormones (see Figure 4, p. 280). Hormones are chemical substances produced in one organ of the body (e.g., the pituitary gland located above the back of the throat) and carried to another organ by the blood stream; they stimulate many processes in the body, including bone growth, muscle development, and the onset of secondary sex characteristics. Secondary sex characteristics (e.g., breast development and the widening of the hips in females, and the increased hairiness and lowered voice pitch in males) are the result of the heightened hormone levels that occur during puberty. These changes are stimulated specifically by two groups of hormones: androgens in males, and estrogens in females. There are several androgenic and estrogenic hormones; the strongest are primarily produced in the gonads (i.e., the testes in men and the ovaries in women) and are called testosterone and estradiol, respectively.
