内分泌系统介绍 Endocrine System Overview.docxVIP

Endocrine System OverviewThe endocrine system, also referred to as the hormone system, is found in all mammals, birds, and fish. It is made up of: Glands located throughout the body. Hormones (i.e., chemical messengers) that are made by the glands and released into the bloodstream or the fluid surrounding cells.Receptors in various organs and tissues that recognize and respond to the hormones. Hormones are released by glands and travel throughout the body searching for cells that contain matching receptors-proteins within the target cell or located on the surface of the target cell. The hormone binds with the receptor, much like a key would fit into a lock to unlock a door. The hormones, or keys, need to find compatible receptors, or locks, to work properly. Although hormones reach all parts of the body, only target cells with compatible receptors are equipped to respond. Once a receptor and a hormone have bonded, the receptor carries out the hormones instructions by either altering the cells existing proteins or turning on genes that will build a new protein. Both of these actions create reactions throughout the body. Researchers have identified more than 50 hormones in humans and other vertebrates.The endocrine system regulates all biological processes from the conception of an organism through adulthood and into old age regulating many functions of a body, including metabolism, blood sugar levels, growth and function of the reproductive system, and the development of the brain and nervous system. The female ovaries, male testes, and pituitary, thyroid, and adrenal glands are all endocrine glands. From Biology: Principles and Explorations, Teaching Transparencies. Copyright 1996 by Holt, Rinehart and Winston. All rights reserved. Reprinted by permission of the publisher.The EPAs Endocrine Disruptor Screening Program focuses on the estrogen, androgen, and thyroid hormones. Estrogens, produced primarily by the ovaries and in small amounts by the adrenal glands, are