In the simplest term, environmental endocrine disruptors (EEDs) are chemical pollutants in the environment that have the potential to affect the endocrine system in animals, especially in humans and wildlife. The endocrine system is a complex network of glands that synthesize and secrete hormones into the circulatory system to coordinate, regulate, and control many of the body's physiologic functions, including reproduction, growth, sexual characteristics, and homeostasis. A hormone, the word meaning to stimulate or to activate, is a chemical signal sent from cells to cells within the same organism; it is a chemical substance with the ability to transmit cellular instructions, and hence often referred to as a chemical messenger.

The objectives of this part (chapter), Part I of the lecture, are for students: (1) to be familiar with the terms and definitions used, especially those pertaining to EEDs; (2) to undertake a brief review of the human endocrine system, which is one of the two major networks regulating our body’s day-to-day function and development; (3) to understand the basic mechanisms of endocrine disruption, which involves one or more biochemical actions or reactions in the endocrine system; and (4) to appreciate the potential effects of endocrine disruption, which at times can even be life-threatening.

The health problems with EEDs are of global concern, mainly due to their vast availability for exposure, which is the topic discussed extensively in Part II continuing into Part III. Meantime, some incidences caused by endocrine disruption have been found to be severe to humans and wildlife. Selected cases are thus provided toward the end of this presentation to strengthen the student’s appreciation of the actual health impacts from these pollutants.