Figure 1.

Block diagram of the thyrotropic feedback control loop with an additional TSH-T₃-shunt, adapted from Ref. (1, 2). Except for G_T3, k, and G_D1, all parameters were adopted from the model in Ref. (1, 2). The parameters G_D1 and G_T3 were estimated to obtain an optimal (in a least squares sense) fit to measured in vivo FT₃-concentrations. To this end, the value of k was normalized to 1 mU/l.