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Endocrine System - ENDOCRINE SYSTEM Chapter 16 Animal body...

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ENDOCRINE SYSTEM – Chapter 16 10/25/07 Animal body made up of trillions of cells 2 basic mechanisms: nervous system sends electrical signals to effector organs endocrine system sends chemical signals (hormones) * Both systems are the two that maintain body functioning Epithelial Tissue forms continuous sheets and layers functions in exchange of materials forms hair, hooves, horns glands are epithelial cell derivatives o exocrine o endocrine – secrete hormones into the body Hormones Greek “to arouse or excite” chemical messengers released by endocrine glands into the blood stream and they exert  their effect some distance away chemical secreted by an endocrine gland that affects the function of target tissues Mode of Transmission Endocrine Epicrine o hormones never enter general circulation Neurocrine o neurotransmitters being released into synaptic cleft Paracrine o hormone diffuses into interstitial fluid of tissue Exocrine Chemical structure of hormones 1. Peptide hormones range from small to large includes hormones from hypothalamus and pituitary gland 2. Amine hormones made up of one or two amino acids
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thyroid hormones --> long-acting hormones tyrozine, epinephrine, and norepinephrine --> short-acting 3. Steroid hormones released from male+female reproductive tract as well as kidneys all steroid hormones are derived from cholesterol example: Cordizone 4. Fatty Acid Derivatives  derived from prostoglandins have an effect on cells around them Hormones can be: Freely circulating o rapidly removed from bloodstream bound to transport proteins *only target cells respond because they have receptors for the hormone Mechanisms of hormone action target cells contain receptors for hormones receptors for catecholamines, peptide hormones, prostaglandins are in the cell  membranes of target cells Thyroid and steroid hormones cross the membrane and bind to receptors in the cytoplasm  or nucleus Modulation of target cell response down   regulation when a hormone is in excess up   regulation when hormone is deficient o target issue more responsive o the number of receptors increases Hormone action must be terminated Half-life   the time it takes for the hormone to go from high concentration to half of  what it was before Control of endocrine activity
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endocrine reflexes are the counterparts of neural reflexes o example – parathyroid hormone  Hypothalamus regulates the activity of the nervous and endocrine systems o secreting regulatory hormones that control the anterior pituitary gland o
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