Physiology of Finfish and Shellfish (2+1)

5.2.2.2. The pituitary gland

Pituitary or the hypophysis is the most important endocrine gland in teleosts and consists of 2 main parts or components, the neurohypophysis (the posterior pituitary), neural part and the adenohypophysis (the anterior pituitary), a glandular part. Of these, neurohypophysis is derived from the brain i.e., from the floor of the embryonic diencephalon (fore brain) and the adenohypophysis develops as an ectodermal evagination of the roof of the buccal cavity. The pituitary gland is present in a shallow depression, the sella tunica which is found in the sphenoidal area of the skull is situated ventral to the brain in the region of diencephalon just behind the optic chiasma (formed by the decussation of the optic nerves) and is connected or functionally linked to the hypothalamus by the pituitary stalk (also named the "infundibular stem", or simply the "infundibulum") which may be absent in some species. It is from the hypothalamus that hypothalamic tropic factors are released to descend down the pituitary stalk to the pituitary gland where they stimulate the release of pituitary hormones. While, the pituitary gland is known as the 'master' endocrine gland because it controls other glands. But both of the lobes are under the control of the hypothalamus ; the anterior pituitary receives its signals from the parvocellular neurons (Parvocellular cells, also called P-cells, are neurons located within the parvocellular layers of the lateral geniculate nucleus (LGN) of the thalamus ) and the posterior pituitary receives its signals from magnocellular neurons (Magnocellular neurosecretory cells are large cells within the supraoptic nucleus and paraventricular nucleus of the hypothalamus).