Lecture 21 - Thyroid Hormone

Lecture 21 - Thyroid Hormone - L ecture 21 Thyroid Hormone...

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Lecture 21 – Thyroid Hormone - - Has affect throughout the body! Biological effects - T4 (4 iodine, inactive) vs T3 (3 iodine, active) vs rT3 (reverse T3)-- (TBL notes) o Organification adding iodine Mechanism of thyroid hormone action - T 3 mediates its action by binding to thyroid hormone receptors - Thyroid hormone receptors are ligand-activated transcription factors acting in the nucleus - T 3 enters cells by specific ATP-consuming carrier- mediated processes. o Specific binding sites on plasma membrane Effects - T 3 stimulates growth, development, and energy metabolism - T 3 influences the function of most organs - o CNS development o linear growth o (modulation of GH expression) - Calorigenesis (thermogenesis) o synthesis of Na + -K + ATPase o uncoupling proteins, basal metabolic rate If people have too much thyroid hormone too much heat! o rate of energy-consuming futile metabolic cycles - Modulation of sympathetic nervous system o cAMP response to catecholamines o β -adrenergic receptor number - Cardiovascular Effects o chronotropism ( HR due to enhanced effect of catecholamines) o ionotropism ( in heart muscle contractility due to induction of α -myosin heavy chain) - Increased Turnover of: o Carbohydrates o Lipids o Cholesterol o Vitamins o muscle protein o bone o cortisol - Energy Metabolism o Basal Metabolic rate ↑ o Core body Temperature ↑ - Organ Effects o Heart - Rate ↑ o Liver - Cholesterol ↓ o Muscle - Protein turnover ↑ o GI tract - Motility ↑ - An individual is known to have a thyroid disorder and is sweaty, shaky and complains of feeling warm. Which is true? o This person will have a tendancy to gain weight over time. o This person likely has a slow heart rate. o This person is at increased risk for bone loss over time (thyroid hormone – catabolic affects; break down to make energy) o This person likely has an iodine-deficient diet. Thyroid Hormone Formation - Spherical follicles lined by cubical epithelial cells - Follicular lumen: o Colloid fluid: contains nascent thyroid molecules attached to scaffolding protein (thyroglobulin o thyroid hormone precursors - Thyroid hormone reserves in colloid and long t½ of thyroid hormone ensure steady hormone delivery despite fluctuations in iodine supply 1) Iodine Uptake into Thyroid Cell - Mediated at baso-lateral side of cell
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Lecture 21 - Thyroid Hormone - L ecture 21 Thyroid Hormone...

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