Endocrine System Summary

Endocrine System Summary - Endocrine System-Summary...

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1 Endocrine System-Summary Hormones: Chemical messengers secreted into the blood by endocrine cells or specialized neurons Classification : 1. Peptide hormones (most hormones are peptides or proteins- Exclusion rule : if a hormone isn’t a steroid or amine, it must be a peptide) 2. Steroid hormones (usually have “–sterone” in name). 3. Amine hormones (derived from single amino acids) Control of Hormone Release A. The target of most trophic hormones is another endocrine gland or cell B. Hormones can be classified by endocrine reflex pathways a. Classic hormone pathways are simplest: endocrine cell acts as receptor and integrating center – directly senses stimulus and responds by secreting hormone b. Hormones most often act as negative feedback signals c. Complex endocrine pathways include two or more hormones (complex reflexes usually involve trophic hormones) d. Some endocrine cells respond to multiple stimuli e. Neurohormones are secreted by neurons into the blood i. Three major groups: 1. posterior pituitary hormones synthesized in hypothalamus 2. trophic hormones from hypothalamus that act on anterior pituitary 3. catecholamines from adrenal medulla C. Multiple hormones can simultaneously affect a single target a. cells and tissue are often under control of multiple hormones at same time b. hormone interactions cannot be predicted based on individual hormone action c. 3 types of hormone interactions : i. Synergism – combined action of hormones A+B > summed action of A alone + B alone (e.g., epinephrine and glucagons) ii. Permissiveness – hormone A will not exert full effect without presence of hormone B (e.g., thyroid hormone and growth hormone) iii. Antagonism – hormone B diminishes the effect of hormone A (e.g., growth hormone or glucagons, both of which increase blood glucose are antagonistic to insulin) The Pituitary Hormones: The pituitary gland is 2 fused glands Anterior Pituitary Anterior pituitary (adenohypophysis; pars distalis) – true endocrine tissue derived from tissue that forms the roof of the mouth (epithelial), synthesizes and secretes six classic hormones 1. prolactin (only one not trophic): development of the breasts and secretion of milk 2. growth hormone – somatotropic hormone – causes growth in almost all cells and tissues A. dwarfism: deficiency of anterior pituitary secretion of growth hormone during childhood; 2/3 do not secrete gonadotropic hormones also
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Endocrine System Summary - Endocrine System-Summary...

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