ANATOMY AND PHYSIOLOGY OF THE ENDOCRINE SYSTEM
The endocrine system is one of two major systems which control the body's
activities. The endocrine system is composed of glands which secrete substances
called hormones into the bloodstream. These hormones act as chemical messengers
and float in the bloodstream to the body's organs, the target of the particular hormone.
At the target, the hormone causes some action. The hormone either turns on a
biochemical reaction or turns off a biochemical reaction.
a. The Endocrine System and the Nervous System. The endocrine system
works with the nervous system to regulate and integrate the processes of the body such
as growth, development, reproduction, response to stress, and change of food into
energy and body tissue. The two systems work together like a giant super system.
Some parts of the nervous system stimulate or prevent the release of hormones. Some
hormones can stimulate or prevent the flow of nerve impulses.
b. Composition and Activities of Hormones. Hormones are composed of
proteins, amino acids, or steroids. Although hormones affect many of the body's
activities, hormone actions can be categorized into four broad areas:
Figure 1-1. General location of major endocrine glands.