The main function of endocrine glands is to secrete hormones directly into the bloodstream. Hormones are chemical substances that affect the activity of another part of the body (target site). In essence, hormones serve as messengers, controlling and coordinating activities throughout the body.

Upon reaching a target site, a hormone binds to a receptor, much like a key fits into a lock. Once the hormone locks into its receptor, it transmits a message that causes the target site to take a specific action. Hormone receptors may be within the nucleus or on the surface of the cell.

Ultimately, hormones control the function of entire organs, affecting such diverse processes as growth and development, reproduction, and sexual characteristics. Hormones also influence the way the body uses and stores energy and control the volume of fluid and the levels of salts and sugar in the blood. Very small amounts of hormones can trigger very large responses in the body.
http://www.merck.com/mmhe/sec13/ch161/ch161c.html

The hormones regulate metabolism, growth and sexual development. These glands release the hormones directly into the bloodstream, where they are transported to organs and tissues throughout the entire body.

When functioning properly, the endocrine system, is like a fine-tuned orchestra. Because the endocrine system is comprised of several organs, many functions can go awry. In this section we'll explain the intricacies of the endocrine system and just how you can "make it play" the music you want it to.

The endocrine system consists of the pancreas, thyroid, parathyroid, adrenals, pineal, pituitary and testes/ovaries. The following diagram shows the relationships between these various organs. As you can easily see, these relationships are complex and it takes a skilled clinician to be able to know just what is wrong when looking at the endocrine system.
http://www.becomehealthynow.com/article/bodyendocrine/732