Figure 1.

Development and function of the pituitary–hypothalamic axis. Pituitary development is initiated with the appearance of the hypophyseal placode, apposed to the future ventral diencephalon. The placode later invaginates to become Rathke's pouch (RP), still in contact in its dorsal most part with the infundibulum, which lies within the ventral diencephalon. The infundibulum then evaginates towards RP. It will give rise to the median eminence, the pituitary stalk and the posterior lobe, while the anterior and intermediate lobes originate from RP. Postnatally, the hypothalamus centralises peripheral information and controls pituitary endocrine secretions through release of hypophysiotrophic hormones. Hypothalamic peptide hormones can reach the gland directly, such as oxytocin and vasopressin secreted directly in the posterior lobe, or via the hypophyseal portal system; peptides (GnRH, gonadotrophin-releasing hormone; GHRH, GH-releasing hormone; TRH, thyrotropin-releasing hormone; CRH, corticotropin-releasing hormone; and the inhibitory SST, somatostatin) are secreted at the median eminence and collected by capillaries (adapted from Rizzoti & Lovell-Badge (2011)). Anterior pituitary endocrine cells comprise lactotrophs (producing prolactin, Prl), gonadotrophs (producing luteinizing hormone, LH; and follicle stimulating hormone, FSH), thyrotrophs (producing thyroid stimulating hormone, TSH), corticotrophs (producing adrenocorticotrophic hormone, ACTH; proteolytically cleaved from proopiomelanocortin, POMC) and somatotrophs (producing growth hormone, GH).