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Thyroid Hormones

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Thyroid Hormones

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    1. 8/31/2012 1 Thyroid Hormones JP Slovak

    2. 8/31/2012 2 Introduction Thyroid gland Highly vascularized Many hollow follicles Each follicle filled with fluid(colloid) Follicle cells secrete hormones C cells - calcitonin

    3. 8/31/2012 3

    4. 8/31/2012 4 Iodide Uptake Principal source is diet Some regions poor source Must supplement Goiters were once common Iodized salt Hypothyroidism a problem in developing countries Most cells can accumulate iodide

    5. 8/31/2012 5 Synthesis of Hormones TSH increases synthetic machinery TSH – immediate activation of hormone synthesis Use cAMP TSH increases iodide incorporation Iodide combines with thyroglobulin T4 and T3 are the liberated forms T4 50x greater than T3 T3 can be formed from T4 outside thyroid T4 may be a prohormone

    6. 8/31/2012 6 Stimulation of Thyroid Receptor binding cAMP Transmembrane ion flux Activation of protein kinases Iodination of thyroglobulin due to hydrogen peroxide generation Increase in colloid droplets Cellular metabolism – pentose phosphate pathway Protein synthesis Iodide influx

    7. 8/31/2012 7

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    9. 8/31/2012 9 Control TSH from pituitary TRH from hypothalamus Stress = decreased TSH Low body temperature = increased TSH in infants T4 controls expression of TRH prohormone

    10. 8/31/2012 10 Growth and Development Absence = slow growth GH decreases in absence of thyroid hromones Stimulate tissue differentiation Stimulate hyaluronidase Hylaluronic acid decrease may signal differentiation Aids in mammary development in mice Aids in myelinogenesis

    11. 8/31/2012 11 Thermogenesis Stimulates oxygen consumption Increases ATP breakdown T3 increases sodium potassium pump Sodium pump theory of thermogenesis

    12. 8/31/2012 12 Diet Increased calories = increased thermogenesis T3 is elevated during overfeeding Increased metabolic rate with CHO consumption Fasting = decreased T3 Food restriction increases longevity

    13. 8/31/2012 13 Permissive Actions Induce GH production Ability of glucocorticoids to stimulate GH Ornithine decarboxylase activity Controls protein bbiosynthesis Needs thyroid hormones

    14. 8/31/2012 14 Mechanism of action Analogous to steroid hormone action TR are intra nuclear receptors Thyroid hormones stimulate RBC Ca-ATPase activity Receptors for T3 and T4 on mitochondria Thyroid hormones act on may cellular receptor sites

    15. 8/31/2012 15 Pathophysiology Hypothyroidism Hyperthyroidism Cretinism Total absence of thyroid hormones Thyroid may fail to develop Symptoms Failure of skeletal growth Development of intellect hindered Goiter

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