Following thyroid gland removal, why does TSH initially rise despite exogenous thyroxine (T4) administration?

💡 Explanation

Following thyroidectomy, TSH rises because administered T4 needs time for conversion to T3 by peripheral deiodinases to exert negative feedback on the pituitary. The pituitary responds more strongly to T3 rather than T4 directly; therefore, TSH secretion persists until T3 levels rise from peripheral conversion of the exogenous T4.

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