Characteristics of the Endocrine System

CHARACTERISTICS OF THE ENDOCRINE SYSTEM

The endocrine system is composed of endocrine glands and spe-cialized endocrine cells located throughout the body (figure 10.1). Endocrine glands and cells secrete minute amounts of chemical mes-sengers called hormones (hor′ mōnz) into the bloodstream, rather than into a duct. 

Figure 10.1  Major Endocrine Glands and Their Locations

Hormones then travel through the general blood cir-culation to specific sites called target tissues or effectors, where they produce a coordinated response of the target tissues. Thus, the term endocrine (en′dō-krin), derived from the Greek wordsendo,mean-ing within, and krino, to secrete, appropriately describes this system.

 Endocrine glands are not to be confused with exocrine glands. Exocrine glands have ducts that carry their secretions to the outside of the body, or into a hollow organ, such as the stomach or intestines. Examples of exocrine secretions are saliva, sweat, breast milk, and digestive enzymes.

 The study of the endocrine system, known as endocrinology