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Anatomy of the Endocrine System

Endocrine System Introduction

The endocrine system is made up of glands that produce and secrete hormones, chemical substances produced in the body that regulate the activity of cells or organs. These hormones regulate the body's growth, metabolism (the physical and chemical processes of the body), and sexual development and function. The hormones are released into the bloodstream and may affect one or several organs throughout the body.

Hormones are chemical messengers created by the body. They transfer information from one set of cells to another to coordinate the functions of different parts of the body.

The major glands of the endocrine system are the hypothalamus, pituitary, thyroid, parathyroids, adrenals, pineal body, and the reproductive organs (ovaries and testes). The pancreas is also a part of this system; it has a role in hormone production as well as in digestion.

The endocrine system is regulated by feedback in much the same way that a thermostat regulates the temperature in a room. For the hormones that are regulated by the pituitary gland, a signal is sent from the hypothalamus to the pituitary gland in the form of a "releasing hormone," which stimulates the pituitary to secrete a "stimulating hormone" into the circulation. The stimulating hormone then signals the target gland to secrete its hormone. As the level of this hormone rises in the circulation, the hypothalamus and the pituitary gland shut down secretion of the releasing hormone and the stimulating hormone, which in turn slows the secretion by the target gland. This system results in stable blood concentrations of the hormones that are regulated by the pituitary gland.

Hormones Regulated by the Hypothalamic/Pituitary System
Hormone Pituitary Stimulating Hormone Hypothalamic Releasing Hormone
Thyroid hormones T4, T3 Thyroid-stimulating hormone (TSH) Thyrotropin-releasing hormone (TRH)
Cortisol Adrenocorticotropin hormone (ACTH) Corticotropin-releasing factor (CRF)
Estrogen or testosterone Follicle-stimulating hormone (FSH), luteinizing hormone (LH) Luteinizing hormone-releasing hormone (LHRH) or gonadotropin-releasing hormone (GnRH)
Insulinlike growth factor-I (IGF-I) Growth hormone Growth hormone-releasing hormone (GHRH)

Illustration of the Endocrine System

Illustration of the endocrine system.

Medically Reviewed by a Doctor on 11/10/2014
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