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Thyroid Hormones

Thyroid Hormones. Hormone cascade. Hypothalamus. TRH. Anterior Pituitary. TSH. Thyroid. T3/T4. Increased BMR and protein synthesis. 6 Steps of T3/4 Production. Thyroglobulin synthesis Uptake and conentration of Iodide (I - )

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Thyroid Hormones

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  1. Thyroid Hormones

  2. Hormone cascade Hypothalamus TRH Anterior Pituitary TSH Thyroid T3/T4 Increased BMR and protein synthesis

  3. 6 Steps of T3/4 Production • Thyroglobulin synthesis • Uptake and conentration of Iodide (I-) • Oxidation of iodide to iodine (I). By TPO – thyroid peroxidase. • Iodination of thyroglobulin. • Coupling of 2 iodinated tyrosine molecules to form T3 or T4 • Secretion

  4. Three forms of thyroid hormones: • T4 – Thyroxin. Less active, bound to TBG strongly. • T3 – Tri-iodothyronine. More active, less bound but lower levels. • rT3 – Reverse T3. Inactived hormone.

  5. Hormones are bound by TBG (Thyroxine Binding Globulin), T4 bound far more strongly. The active hormone is the free hormone. Despite there being less free T3 it is more active than T4 so has more effect. The shortened half life means it will have a temporary effect.

  6. Deiodinases • Type I – Extracellular. Converts T4 -> T3. Raise in local T3. • Type II – Intracellular. T4 -> T3. Mainly in CNS and pituitary. • Type III – Extracellular. T4 -> rT3. CNS and pituitary. May be protective.

  7. MCT8 / 10

  8. T4 -> T3 2 1 T4-T3 3 T4 -> rT3

  9. Altered Protein Synthesis Affects Transcription Thyroid Hormone Response Change in mRNA

  10. Effects of Thyroid Hormone • Metabolism – Affects anabolic and catabolic. Increased BMR • Maturation and Differentiation. • Neurological Functions – Synapse formation, myelinogenesis, neuronal outgrowth • Growth – mainly GH but needs T3/4

  11. Changes in O2 consumption • Resting – around 250ml/min • No T3 – around 150ml/min • Excess T3 – around 400ml/min • Raised O2 consumption increases ventilation, cardiac output. Use of substrates changes protein/lipid/carbohyrate metabolism. • Heat production, weight loss. Lowered muscle mass, increases urea, increases kidney function.

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