File:Human thyroid system and neural development.jpg

Human Thyroid System Development

Timeline of human thyroid system and brain development from conception to birth. Estimation of neurogenesis adapted from Bayer et al. <pubmed>8361683</pubmed>

Development of the human thyroid gland begins in the third week of gestation (2) (Figure 1, grid 1). On gestation day (GD) 16-17, the embryonic thyroid is visible as an outgrowth in the floor of the primitive buccal cavity (the site of the future pharynx). Additional lateral contributions to the embryonic thyroid originate from a portion of the fourth pharyngeal pouches; these lateral contributions are the origin of the C-cells, which produce calcitonin. The thyroid gland tissues merge and migrate to their final location by GD45-50. By GD70, the thyroid gland is well developed; it begins concentrating iodide and producing thyroid hormone at this time (3). Thyroglobulin (TBG), the precursor protein upon which thyroid hormone is produced and stored, is present as early as GD29 in thyroid follicle cells (2). As the thyroid follicle cells mature, TBG levels are detected in fetal serum by gestation week 11 and increase through gestation (4).

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