The endocrine system helps to maintain internal homeostasis through the use of endogenous chemicals known as hormones. A hormone is typically regarded as a chemical messenger that is released into the bloodstream to exert an effect on target cells located some distance from the hormonal release site.1,2 Various endocrine glands manufacture and release specific hormones that help regulate physiological processes such as reproduction, growth and development, energy metabolism, fluid and electrolyte balance, and response to stress and injury.1,3
The use of drugs to help regulate and control endocrine function is an important area of pharmacology. In one sense, hormones can be considered drugs that are manufactured by the patient's body. This situation presents an obvious opportunity to use exogenous chemicals to either mimic or attenuate the effects of specific hormones during endocrine dysfunction.
Patients can take drugs as replacement therapy during hormonal deficiency—for example, insulin administration in diabetes mellitus. Likewise, exogenous hormone analogs can accentuate the effects of their endogenous counterparts, such as using glucocorticoids to help treat inflammation. Conversely, drugs can treat endocrine hyperactivity—for example, the use of antithyroid drugs in treating hyperthyroidism. Finally, drugs can regulate normal endocrine function to achieve a desired effect, as is done through the inhibition of ovulation by oral contraceptives.
The purpose of this chapter is to review the basic aspects of endocrine function, including the primary hormones and their effects. The factors regulating hormonal release and the cellular mechanisms of hormone action are also briefly discussed. Finally, the basic ways in which drugs can be used to alter endocrine function are presented. This overview is intended to provide you with a general review of endocrine and hormone activity. Chapters 29 through 32 deal with the physiology and pharmacology of the hormones of specific endocrine systems in more detail along with the specific endocrine drugs, and the problems the drugs treat.
PRIMARY ENDOCRINE GLANDS AND THEIR HORMONES
The primary endocrine glands include the hypothalamus, pituitary, thyroid, parathyroid, pancreas, adrenal, and gonads (Fig. 28-1). These glands and the physiological effects of their hormones are also summarized in Tables 28-1 and 28-2. For the purpose of this chapter, only the primary endocrine glands and their respective hormones are discussed. Substances such as prostaglandins and kinins, which are produced locally by a variety of different cells, are not discussed here but are referred to elsewhere in this text (e.g., see Chapter 15). Also, chemicals such as norepinephrine, which serve a dual purpose as hormones and neurotransmitters, are discussed in this chapter only with regard to their endocrine function.
The primary endocrine glands.
Table 28-1HYPOTHALAMIC AND PITUITARY HORMONES