Hypothalamic–pituitary–gonadal axis controls development, reproduction, and aging in animals. Gonadotropin-releasing hormone (GnRH) is secreted from the hypothalamus by GnRH-expressing neurons. The anterior portion of the pituitary gland produces luteinizing hormone (LH) and follicle-stimulating hormone (FSH), and the gonads produce estrogen and testosterone. In oviparous organisms (e.g. fish, reptiles, amphibians, birds), the HPG axis is commonly referred to as the hypothalamus-pituitary-gonadal-liver axis (HPGL-axis) in females. Many egg-yolk and chorionic proteins are synthesized heterologously in the liver, which are necessary for oocyte growth and development. Examples of such necessary liver proteins are vitellogenin and choriogenin. The HPA, HPG, and HPT axes are three pathways
Pituitary gland anterior pituitary. These various parts are separated by meningial membranes, suggesting that the pituitary of other vertebrates may have formed from the fusion of a pair of separate, but associated, glands. Most armadillos also possess a neural secretory gland very similar in form to the posterior pituitary, but located in the tail and associated with the spinal cord. This may have a function in osmoregulation. There is a structure analogous to the pituitary in the octopus brain. Although rudimentary in humans (and often considered part of the anterior pituitary), the intermediate lobe located between the anterior and posterior pituitary is