Endocrine System.

Essay by the_great_tso18University, Bachelor'sF, December 2005

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What Is the Endocrine System?

The foundations of the endocrine system are the hormones and glands. As the body's chemical messengers, hormones (pronounced: hor-moanz) transfer information and instructions from one set of cells to another. Many different hormones move through the bloodstream, but each type of hormone is designed to affect only certain cells.

A gland is a group of cells that produces and secretes, or gives off, chemicals. A gland selects and removes materials from the blood, processes them, and secretes the finished chemical product for use somewhere in the body. Some types of glands release their secretions in specific areas. For instance, exocrine (pronounced: ek-suh-krin) glands, such as the sweat and salivary glands, release secretions in the skin or inside the mouth. Endocrine glands, on the other hand, release more than 20 major hormones directly into the bloodstream where they can be transported to cells in other parts of the body.

The major glands that make up the human endocrine system include the:

* hypothalamus

* pituitary gland

* thyroid

* parathyroids

* adrenal glands

* pineal body

* reproductive glands (which include the ovaries and testes)

The hypothalamus (pronounced: hi-po-tha-luh-mus), a collection of specialized cells that is located in the lower central part of the brain, is the main link between the endocrine and nervous systems. Nerve cells in the hypothalamus control the pituitary gland by producing chemicals that either stimulate or suppress hormone secretions from the pituitary.

Although it is no bigger than a pea, the pituitary (pronounced: puh-too-uh-ter-ee) gland, located at the base of the brain just beneath the hypothalamus, is considered the most important part of the endocrine system. It's often called the "master gland" because it makes hormones that control several other endocrine glands. The production and secretion of pituitary hormones can...