(Ferritin) (319- Ganong22nd) (360- K.S 4th) (689. A.K. Jain 3rd) (304-5- Ganong 23rd)* Iodine (I2) is the raw material essential for thyroid hormone synthesis* Total I' entering ECF is 600|igm/day (500 + 40 + 60) of which, 120 mmg/day (20%) enters the thyroid and 480 mg/day (80%) is excreted in urine* Normal T/S ratio is 25-50:1* T4 deficiency during development causes mental retardation and molar rigidity and deafnessSynthesis of Thyroid hormonesSteps of synthesis of thyroid hormones1. Thyroglobulin synthesis2. Iodide trapping or iodide pump3. Oxidation of iodide4. Iodination of tyrosine5. Coupling reactionsTSH - secreted by anterior pituitary is the major factor regulating the synthesis and release of thyroid hormones.It is also necessary for the growth and secretory activity of the thyroid glands.TSH not only stimulate the secretion of stored thyroid hormones from follicular colloid but it also promotes synthesis of fresh thyroid hormones.