Development of the Brain and the Thyroid Gland

Overview

Thyroxin and triiodothyronine (T4 and T3) are crucial for the satisfactory morphological and functionaldevelopment of the central nervous system during the intrauterine and postnatal period. Contemporary embryologicalknowledge stratifies the development of cerebral structures into time zones and associations and thus it isknown during which week of gestation a certain section is formed. The association between the availability of T3in the nuclei of neurones and glial cells at the correct time and in the correct amount and implementation of thesequence of development of essential brain structures has been already proved. Mechanisms are also known whichregulate the transport of maternal T4 to the cells of the embryo and foetus and the subsequent sophisticated partplayed by deiodases which regulate very sensitively the local production of T3. The prerequisite of these objectivesis however proper function of the maternal thyroid in particular during the first half of pregnancy. The iodinerequirement during pregnancy is high. After delivery when the development of the CNS proceeds and the childmust ensure his own formation of T4 and T3, the need of a permanent iodine supply persists. The adaptationalpower of the sodium-iodide symporter (NIS) in thyrocytes of lactating women ismore than doubled. Care of properthyroid function is necessary not only in women of fertile age, however, the sequealae of hypothyroxinaemia aremost serious in the latter and are irreparable in the child.

Key words:
stages of CNS development, role of T3, transplacental T4 transport, deiodases, hormonogenesis ofthe foetus, recommendations for practice