ABSTRACT

Parathyroid Function .................................................................................. 679 17.5 Adrenal Glands ..................................................................................................................... 679

17.5.1 Normal Structure and Function ................................................................................ 679

The endocrine system is one of the body’s major homeostatic control systems whose aim is to maintain normal function and development in the face of a constantly changing environment. Working in tandem with the nervous system, which is mainly responsible for rapid and immediate responses, the endocrine system tends to act in a slower and more sustained manner to regulate a diverse set of processes. Multiple endocrine glands also work in concert with one another to form complex feedback loops, which tightly regulate critical physiological processes. Like all homeostatic control systems, the capacity to maintain physiological parameters within normal bounds is nite, and when this capacity is exceeded by chemical or drug exposure, or environmental stressors, adverse consequences can ensue. Chemicals can cause endocrine abnormalities via different mechanisms, including direct alteration of hormone production, changes in the regulation of the hormonal axis, effects on hormonal transport, binding and signaling, as well as similar changes to counterregulatory hormone systems. The objective of this chapter is to provide a broad overview of common spontaneous morphological changes in endocrine organs (pituitary gland, adrenal glands, thyroid gland, parathyroid gland, and the pancreatic islets), with examples of xenobiotic-induced changes, predominantly in rodents.