Diagram of the mechanism for Thyroid Hormone Synthesis (T3 + T4)

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  1. Iodide is actively transported into the follicular cell
  2. Iodide is oxidized to Iodine in the colloid
  3. The follicular cell synthesizes Thyroglobulin (TGB) and sends it to the colloid
  4. The tyrosine is Iodated to make T1 and T2.
    1. T2 combines with T1 to make T3.
    2. T2 combines with T2 to make T4(T1 never combines with T1)
  5. T3 and T4 is transported back into the follicular cell where a lysosome digests any colloid
  6. T3 and T4 are released into the bloodstream with TGB and travel to their target cells
  7. Elevated T3/T4 negatively feeds back to the hypothalamus to stop release of TRH