Ch. 17 ENDOCRINE.docx - CHAPTER 17 ENDOCRINE SYSTEM...

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CHAPTER 17 ENDOCRINE SYSTEM Chemical messengers from both the nervous system and the endocrine system are the primary regulators of ALL the activities of the body AND allow cells to communicate with each other to maintain this regulation. Most chemical messengers are produced by a specific collection of cells or by a gland . GLAND = an organ consisting of epithelial cells which specialize in secretion (controlled release of chemicals from a cell). The ENDOCRINE system is composed of glands and cells that secrete the chemical signals called hormones into the plasma of the blood. 4 CLASSES of CHEMICAL MESSENGERS: 1) Autocrine - stimulates the cell that originally secreted it. 2) Paracrine - act locally on neighboring cells and secrete chemicals into the extracellular fluid and affects the surrounding cells (like histamine). 3) Neurotransmitters - secreted by neurons that activate an adjacent cell; secreted into a synaptic cleft 4) Endocrine - secreted into the bloodstream by certain glands and cells & travel through the general circulation to their target cells. The ENDOCRINE SYSTEM is composed of endocrine glands and specialized endocrine cells located throughout the body. Endocrine glands secrete very small amounts of chemical messengers called hormones into the bloodstream. Hormones circulate through the bloodstream to specific sites called target tissues, or effectors. At their target tissues, hormones stimulate a specific response. Hormones have a role in most physiological processes in the body. However, the endocrine system does not work completely alone for every process it regulates. It works with the body’s other major regulatory system, the nervous system.
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