ABSTRACT
Endocrine glands are hormone-producing organs derived from different germ layers. Hormones are released into the blood and regulate specific functions in target organs.
THE HYPOPHYSIS (FIGURES 12.1-12.5) The hypophysis is an ecto-neuroectodermal endocrine gland developing at the site of the midline primary ectoneuroectodermal adhesion anterior to the rostral end of the notochord. In early somite embryos, the adhesion attaches the ectodermal head fold to the bottom of the prosencephalon (future diencephalon). As mesenchyme penetrates into the prechordal area of the head (at stage 7-1), the midline portion of the head fold adherent to the diencephalon changes into Rathke’s pouch, the primordium of the anterior hypophyseal lobe communicating temporarily with the primitive oral cavity. Later, in embryos 10-12 mm long (stage 7-2), the diencephalic neuroectodermal evagination appears adjacent to the posterior wall of Rathke’s pouch, representing the primordium of the posterior hypophyseal lobe (neurohypophysis). Consequently, the anterior wall of Rathke’s pouch gives rise to the pars tuberalis and pars distalis, and the posterior wall of Rathke’s pouch to the pars intermedia of the anterior hypophyseal lobe (adenohypophysis) and becomes separated from the pharynx. The diencephalic neuroectodermal evagination changes into the infundibulum, the hypophyseal stalk and the posterior hypophyseal lobe (neurohypophysis).
