**7. Conclusion**

144 Thyroid Hormone

30 PND Complete

maturation of thyroid gland. E14- E19/20

E15/16- E20



expression which increases gradually towards hatching, expression of TRβ shows an abrupt elevation in late development, especially in

low in kidney.


the cerebellum.

either DI or DII. E17-E20 - The levels of DIII activity

hatching. E18–E20 - Brain DII activity is

E19-E20 - The low T3/T4 ratio is

E20-C0 - DI activity gradually

layer.

C1 (first day posthatch)

increases, reaching a maximum around these period, and decreases slowly to posthatch levels thereafter.



present in liver are rapidly drop by more than 90%. - DI levels in testis and ovary strongly decrease around

moderately decreased, whereas DIII activity is low.

associated with high T3 breakdown in liver and with high T4 inactivation or T3 secretion in kidney.

The actions of THs are highly pleiotropic, affecting many tissues at different developmental stages. As a consequence, their effects on proliferation and differentiation are highly heterogeneous depending on the cell type, the cellular context, and the developmental or transformation status.

Maternal THs are important in promoting normal fetal development especially the placental and CNS development. Clinical epidemiological and basic findings clearly show that maintaining normal TH regulation from the beginning of pregnancy is important to reduce the risk of obstetric complications and to ensure optimal neurodevelopment of the offspring.

In normal pregnancy, transplacental TH passage is modulated by plasma membrane THTs, Ds, sulfotransferases, TRs and several different proteins within placental cells.

In pathological/abnormal pregnancies with either maternal or fetal THs disturbances (hypoor hyper-thyroidism), the placenta lacks the full compensatory mechanisms necessary to optimize the maternal–fetal transfer of THs to achieve the normality of TH levels in the fetus.
