Thyroid 1

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  • 1. DR. LAXMIKANTA SAY
  • 2.  “Thyreos” - “A shield”  Largest endocrine gland  Development – floor of pharynx & thyroglossal duct  Wt. 15 – 20 gms  Highly vascular – 5 ml/gm/min  Thyroglobulin - Mol. Wt. 6,60,000
  • 3.  Functions of Thyroid  Maintains Metabolism in tissue - stimulate O2 consumption - regulate lipid & Carbohydrate metabolism - influence body mass & mentation  Secretion of Calcitonin - regulates Calcium levels
  • 4. BLOOD SUPPLY HISTOLOGY
  • 5.  T4  T3  RT3  Calcitonin
  • 6. Thyroid Cellular Mechanism 1.Iodine trapping  2.Oxidation & Iodination  3.Coupling  4.Release 
  • 7. In Thyroglobulin molecule in colloid MIT-23%  DIT-33%  T3-7%  T4-35%  RT3- Traces 
  • 8. THYROID 4µg/dl 27µg/dl 80µg/dl T4 T3 31µg/dl 2µg/dl 36µg/dl RT3 17μg/dl 38µg/dl
  • 9.   T3 & T4 exist in both free & protein bound form Total plasma T4=8 µgm/dl , T3=0.15 µgm/dl Plasma protein TBG Conc. of T4 Half Life PP (mg/dl) 5 days 2 67% 46% TT 2 days Albumin 13 days T3 15 20% 1% 3500 13% 53%
  • 10. - T4 97% of T4 is secreted from thyroid 99.98 % plasma bound Plasma conc. 2 ng/dL Half-Life – 6-7 days Longer duration of action. Volume of distribution – 15% of body wt.(10L) Prohormone - metabolically inert until deiodinated - 1/3 rd metabolized to T3 & 45% to RT3. - Liver – Sulphation & Glucoronidation - Daily loss in stool – 4-5%
  • 11. T3 - Normal Plasma level – 0.15 µg/dL TBG – 99.8% 0.2% free (0.3ng/dL) Half-Life – 1-2 days More potent & more active. 13% of circulating T3 is by Thyroid 87% deiodination of T4.
  • 12.     Release of T3 & T4 Deiodinase (D1/D2/D3) - a.a selenocycsteine Factors affecting deiodination - fetal life, - drugs, - selenium, - illness, - fasting, Plasma t1/2 - T4-6-7days, T3 -1-2days
  • 13. (+) Cold  (-) heat, stress, T3,T4  TRH SECRETION (+) T3, T4  (-) glucocortiod, dopamine, stress, somatostatin,  T3, T4  TSH SECRETION
  • 14.  Glycoprotein  Secretion of 211 aminoacids. is pulsatile – midnight secretion  Normal secretion - 110 µgm/ day  Plasma level – 0.2–5.0 µ IUunit/ml  Half Life – 60 min.
  • 15.  Salivary gland,  Gastric mucosa,  placenta,  Cilliary body,  Choroid plexus,  Mammary gland