ABSTRACT
Natural processes are regulated by hormonal systems. Within the animal kingdom endocrine glands secrete hormones that serve this purpose. In mammals, the thyroid, pituitary, and adrenal glands all produce them, as do the pancreas, testes, and ovary. Once secreted, these hormones find their way to receptors, such as the androgen and estrogen receptors, and elicit physiological and biochemical responses (see Box 15.1).
