Toxicology of the Endocrine System

The endocrine system plays a critical role in regulating virtually every aspect of the body's functions and systems, including behaviour, nutritional processes, reproduction, growth and development, gastrointestinal tract, cardiovascular system and homeostasis. It includes various endocrine glands, for example, hypothalamus, pituitary, adrenals, gonads, thyroid and pancreas, that secrete specific hormones (or messengers) as well as specific receptors in target organs throughout the body, which are activated or deactivated by a series of biochemical reactions upon contact with the proper hormone, which ultimately modifies the target organ's activity. This is a complex and interactive system and malfunctions may have serious consequences. Disorders can arise internally from overactive or underactive hormone production, or they can arise from external exposures. Both can have life-threatening effects on survival. It has been shown that many drugs and chemicals and some environmental chemicals can perturb the chemical balance of the endocrine system. Some chemicals may directly affect the normal function of the endocrine system by inhibiting specific enzymes, while others produce indirect effects that result in a pharmacological interaction between the hormone and the chemical which modulates the effect of the hormone. There are many variations on these mechanisms and effects and these are detailed in this chapter. Keywords: endocrine toxicology; hormones; biochemical regulation; endocrine disruptors; endocrine modulation; endocrine receptors; endocrine target organs