What is it about?
This review article on thyroid homeostasis summarizes theories of hypothalamus-pituitary-thyroid interaction. It is based on principles of systems medicine, biological cybernetics and biochemistry. Special emphasis is laid on on thyrotropin and other thyroid stimulators. In addition, it summarizes the role of calculated structure parameters like SPINA-GT, SPINA-GD or Jostel's TSH index for evaluation of thyroid function.
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Why is it important?
This is the first review article that summarizes efforts in mathematical and cybernetic modelling of thyroid homeostasis.
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This page is a summary of: TSH and Thyrotropic Agonists: Key Actors in Thyroid Homeostasis, Journal of Thyroid Research, January 2012, Hindawi Publishing Corporation,
DOI: 10.1155/2012/351864.
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Figure 1
Information processing structure of the logarithmic standard model of thyroid homeostasis
Figure 2
Information processing structure of a nonlinear parametrically isomorphic model based on Michaelis-Menten kinetics, noncompetitive divisive inhibition, and pharmacokinetic data.
Figure 3
SimThyr, a continuous simulation program for thyrotropic feedback control
Figure 4
Characteristic curves of pituitary and thyroid. The area shaded in green denotes univariate reference ranges for TSH and FT4. The dashed red line denotes the pituitary’s response in form of TSH incretion to varying FT4 levels; the continuous blue line represents the thyroid’s response to TSH. Note that for the response curve of the thyroid—contrary to convention—the ordinate (TSH) is the independent axis, while the dependent axis is the abscissa (FT4).
Figure 5
Successive development of hypothyroidism as a consequence of decreasing . Beginning with a hypothetical “sublatent” form defined by reduced GT and still normal levels of TSH and FT4 (panel b), further steps are subclinical hypothyroidism with increased TSH levels and FT4 still in the lowest fraction of the reference region (panel c) and overt hypothyroidism where both parameters have left their reference region (panel d).
Figure 6
Partial and complete thyrotropic insufficiency as results of nonlinear interaction of pituitary and thyroid. TSH axis is logarithmically scaled in order to zoom small values. GH values are given in percent from normal values
Figure 7
Computer simulation of thyrotropic adaptation in critical illness. A gradual increase of central type 2 deiodinase activity over several days with subsequent restoration to normal values has been simulated with SimThyr using the mathematical model shown in Figure 2. Note the temporarily increased TSH values after day 17 that are occasionally observed also in vivo in patients recovering from nonthyroidal illness syndrome.
Figure 8
Interaction of TSH, thyrotropic agonists, and thyrotropic antagonists with TSH receptor. SMLs bind to a pocket within the heptahelical transmembrane domain, while TSH, HCG, and TRAbs bind primarily to the TSHr amino-terminal ectodomain.
Figure 9
Comparison of conventional univariate reference ranges for TSH and FT4 (grey box) and a bihormonal reference region (green kite-like area) from nonlinear modelling of thyroid homeostasis.
SimThyr simulation software
SimThyr, a simulator of thyroid homeostasis.
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