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What does T4ORD stand for?

T4ORD stands for T4 outer-ring deiodination to T3


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In healthy human subjects with an adequate iodine intake, the thyroid gland produces predominantly the prohormone T4 and a small amount of the bioactive thyroid hormone T3. Roughly 80% of T3 is produced by outer ring deiodination (ORD) of T4 in peripheral tissues. The relative contribution of T3 secretion increases in iodine deficiency and other conditions where the thyroid gland is stimulated by TSH or TSH receptor antibodies, since this is associated with increased de novo T3 synthesis and thyroidal expression of both D1 and D2, and thus increased intra-thyroidal T4 to T3 conversion (see below).
The changes that occur in thyroid function tests with advancing age. There is an age-dependent decline in serum TSH and (free) T3. The reduction in TSH secretion may very well be due to an increased sensitivity of the thyrotrophes to the negative feedback by T4, but other factors such as a reduced hypothalamic TRH secretion cannot be excluded (shown in purple). Although reduced TSH levels result in a reduced thyroidal T4 secretion in the elderly, serum total and free T4 (FT4) concentrations remain unchanged. This is because T4 degradation by outer ring deiodination.