Ch 16 Endocrine System

Ch 16 Endocrine System - Ch. 16: The Endocrine System The...

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Ch. 16: The Endocrine System The Nervous System and the Endocrine System together act to direct the maintenance of homeostasis – in other words, to control internal conditions. Control by the Nervous System is rapid, localized (via nerve impulse transmission) and relatively short-lived. Control by the Endocrine System is slower, more global (hormones distributed through circulatory system) and more prolonged. I. Overview of Endocrine System and Hormone Function A. Endocrine organs 1. Contain ductless glands which secrete by merocrine secretion 2. Are well-vascularized: hormones secreted enter bloodstream directly 3. Small and widely separated in the body B. Major endocrine organs 1. Pituitary 2. Thyroid 3. Parathyroids 4. Adrenals 5. Pineal 6. Thymus C. Organs w/some endocrine function 1. Pancreas 2. Gonads 4. Kidneys 5. Heart 6. Placenta 7. Some cancerous tumors (lung, pancreas) D. Hormonally regulated processes include 1. Reproduction 2. Growth and development 3. Stress Response 4. Maintenance of Fluid and Electrolyte Balance 5. Maintenance of Nutrient levels and delivery 6. Regulation of cellular metabolism II. Hormones ( hormon = to excite) A. Hormones 1. Functional definition : chemical substances, secreted by cells into extracellular fluids, that regulate metabolic function of other cells in the body. Hormones alter cell activity by stimulating or inhibiting characteristic cellular processes Cell responses to hormone stimulation include changes in Membrane permeability Activation or inhibition of enzyme synthesis Secretory activity Etc. 2. Chemical structure : a. Steroids (derived from cholesterol; ex testosterone, cortisol) b. Peptide/Protein (ex insulin, growth hormone) c. Amino Acid derivatives (ex thyroid hormones, epinephrine)
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B. Hormone-target cell specificity : 1. Receptor-dependent ---> hormones can only affect cells which have receptors for them 2. 3 Factors determine extent of target cell activation : Blood levels of the hormone Relative # of receptors for that hormone on target cell Strength of interaction btwn hormone & receptor 3. Hormone receptors dynamic structures ---> changes in #, sensitivity responsive to hormone levels C. Mechanisms of Hormone Action 1. Second messenger mechanisms a. Example of a 2 nd messenger system: cAMP 1) 1 st messenger (=hormone) binds to mmb receptor on outside of cell 2) Receptor is coupled to a “transducer” on inner side of mmb(called a G- protein) 3) Hormone binding causes receptor to activate G-protein 4) Activated G-protein “turns on” intracellular enzyme (adenylate cylase) 5) Increased enzyme activity = increased cAMP (2 nd messenger) levels 6) 2 nd messenger initiates a series of enzymatic rxns that alter cell metabolism For every hormone binding event, many more molecules of cAMP are produced => amplification (small amt hormone = large effect on cell)
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Ch 16 Endocrine System - Ch. 16: The Endocrine System The...

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