Homeostasis depends on the precise regulation of the organs and organ systems of the body. Together the nervous and endocrine systems regulate and coordinate the activity of nearly all other body structures. When either the nervous or endocrine system fails to function properly, conditions can rapidly deviate from homeostasis.

Disorders of the endocrine system can result in diseases like insulindependent diabetes and Addison's disease. Early in the 1900s, people who developed those diseases died. No effective treatments were available for those and other diseases of the endocrine system, such as diabetes insipidus, Cushing's syndrome, and many reproductive abnormalities. Advances have been made in understanding the endocrine system, so the outlook for people with these and other endocrine diseases has improved. The endocrine system is small in size compared to its importance to healthy body functions. It consists of severalsmall glands distributed throughout the body that could escape notice if not for the importance of the small amounts of hormones they secrete.

This chapter first explains the functions of the endocrine system (p. 610) and then profiles the pituitary gland and hypothalamus (p. 610), hormones ofthe pituitary gland (p. 613), thyroid gland (p. 619), parathyroid glands (p. 624), adrenal glands (p. 627), and pancreas (p. 632). It then moves to discussions about hormonal regulation of nutrients (p. 637), hormones of the reproductivesystem (p. 639), hormones of the pineal body (p. 640), hormones of the thymus (p. 640), and hormones of the gastrointestinal tract (p. 640), and hormonelikesubstances (p. 640). The chapter concludes with a look at the effects of agingon the endocrine system (p. 642).