The fetal endocrine system is functional for some time before the central nervous system reaches maturity (Mulchahey, 1987). he anterior pituitary gland develops from oral ectodermRathke pouch, whereas the posterior pituitary gland derives from neuroectoderm. As with other organ systems, embryonic development involves a complex and highly spatiotemporally regulated network of signaling molecules and transcription factors (Bancalari, 2012; de Moraes, 2012).
Anterior and Intermediate Lobes. The adenohypophysis, or anterior pituitary, diferentiates into five cell types that secrete six protein hormones. Of these types, lactotropes produce prolactin (PRL), somatotropes produce growth hormone (GH), corticotropes produce adrenocorticotropic hormone (ACTH), thyrotropes produce thyroid-stimulating hormone (TSH), and gonadotropes produce luteinizing hormone (LH) and folliclestimulating hormone (FSH).
ACTH is irst detected in the fetal pituitary gland at 7 weeks, and GH and LH have been identified by 13 weeks. By the end of the 17th week, the fetal pituitary gland synthesizes and stores all pituitary hormones. Moreover, the fetal pituitary is responsive to tropic hormones and is capable of secreting these early in gestation (Grumbach, 1974). he fetal pituitary secretes �-endorphin, and cord blood levels of �-endorphin and �-lipotrophin rise with fetal PC02 (Browning, 1983).
The intermediate lobe in the fetal pituitary gland is well developed. The cells of this structure begin to disappear before term and are absent from the adult pituitary. he principal secretory products of the intermediate lobe cells are .-melanocytestimulating hormone (.-MSH) and �-endorphin.
Neurohypophysis. The posterior pituitary gland or neurohypophysis is well developed by 10 to 12 weeks, and oxytocin and arginine vasopressin are demonstrable. Both hormones probably unction in the fetus to conserve water by actions directed largely at the lung and placenta rather than kidney. Vasopressin levels in umbilical cord plasma are increased strikingly compared with maternal levels (Chard, 1971).
This gland arises from the endoderm of the second pharyngeal pouch. he thyroid migrates to its inal position and the obliterated thyroglossal duct connects to the foramen cecum of the tongue. he pituitary-thyroid system is functional by the end of the first trimester. The thyroid gland is able to synthesize hormones by 10 to 12 weeks, and thyrotropin, thyroxine, and thyroid-binding globulin (TBG) have been detected in fetal serum as early as 11 weeks (Bernal, 2007). he placenta actively concentrates iodide on the fetal side, and by 12 weeks and throughout pregnancy, the fetal thyroid concentrates iodide more avidly than does the maternal thyroid. hus, maternal administration of either radioiodide or appreciable amounts of ordinary iodide is hazardous after this time (Chap. 58, p. 1121). Normal fetal levels of free thyroxine (T4), free triiodothyronine (T3)' and thyroxin-binding globulin increase steadily throughout gestation (Ballabio, 1989). Compared with adult levels, by 36 weeks, fetal serum concentrations of TSH are higher, total and free T3 concentrations are lower, and T4 is similar. This suggests that the fetal pituitary may not become sensitive to feedback until late pregnancy (horpeBeeston, 1991).