It is formed by a group of nuclei, scattered in the walls and floor of third ventricle.
PITUITARY GLAND IN VERTEBRATES
MAMMALS
FUNCTION
It stimulates the nephron to reabsorb water from the urine and thus it reduces the volume of urine formed. OXYTOCIN : it cause the contraction of the mammary gland resulting in the ejection of milk.
REPTILES
Anterior pars distalis surrounds a part of upper portion of neurohypophysis and posterior pars distalis surrounds the lower part of .. neurohypophysis and also anterior region of pars intermedia. Pars intermedia : The pars intermedia surround the .. posterior region of neural lobe more or less completely as an enclosing cup. It is thick with many cellular layers .. making a massive glandular structure more or less equal to that of pars distalis in size.
HORMONES SECRETED BY PITUITARY GLAND
Each of the hormones are produced by seperate type of cell within the pituitary gland, except for FSH and LH. A hormone produced by intermediate pituitary gland is melanocyte stimulating hormone , which act on skin to stimulate to produce melanin.
BIRDS
Anterior pituitary gland separated - cephalic lobe & caudal lobe and it makes up most of adenohypophysis .It ventrally situated yo the neurohypophysis. It release a number of hormones : TSH - stimulates the thyroid Adenocorticotrophic hormone - stimulates the adrenal cortex Sex hormones - stimulates the sex glands Luteinising hormone Follicles stimulating hormone. Posterior pituitary gland consists of neuro secretory terminals Posterior pituitary gland produces arginine vasotocin & stores oxytocin ( me so to in ) and antidiuretic hormone ( ADH which is known as vasopressin) that are produced by hypothalamus.
Stimulates the thyroid glad - important role in metabolism Pituitary gland receives signals from the hypothalamus and then. Prolactin hormone: Essential - expression of parental care in birds High levels have been shown to stimulate. Feeding: Prolactin stimulates - growth & development of specialized epithelial cells lining the cropsac of pigeons and doves Leading to formation of " crop milk" - fed to the newly hatched aquab.
Brooding: Prolactin - stimulate & regulate the broodiness Birds develop- brood patch - an area of bare , featherless skin on the underbody - preparation for incubation &. After the hatch - parent birds brood their young, keeping them warm by spreading the feathers out , umbrella like - young can maintain contact with the skin of the adult. Posterior pituitary gland produces - arginine vasotocin and stores oxytocin and antidiuretic hormone Oxytocin - release of the yolk into the oviduct and the actual laying of the egg or ovoposition Antidiuretic - kidney collecting.
AMPHIBIANS
In lower vertebrates the stalk and the pars nervosa and hollow out by a central canal,continuous with the third ventricle being the remnant of the original lumen of the nervous downgrowth. The posterior lobe is formed of pituicytes,non –medullated nerve fibres,mast cells,herring bodies and blood vessels.
FUNCTIONS
GROWTH HORMONES
ACTH: ACTH stimulates the adrenal cortex inducing hypertrophy particularly of the zona fasciculata and causing secretion of glucocorticoids. Hypophysial secretion of ACTH is normally regulated by the hypothalamus which condition in turn, is influenced by blood filter of the corticosteroid. In stress,the accelerated secretion of ACTH is the part neurally effected by way of hypothalamus,in ;part by the exciting action of adrenaline on the hypothalamic centre as well as the gland itself.
The secretion of MSH is depressed by glucocorticoids as the cases of adrenocortical insufficiency are subjected to. When the pituitary gland removed from a frog it results in the permanent bleaching of the skin.
FISH
The pituitary gland is located below the diencephalon (hypothalamus), behind the optic chiasma and anterior to saccus vasculosus, and is attached to the. diencephalon by a stalk or infundibulum. Usually in cyclostomes it is smaller but increases in bony fishes, with prominence in groove or depression of para- sphenoid bone receiving the gland. turcica comparable to that found in mammals in. Microscopically, the pituitary gland is composed of two parts:. i) Adenohypophysis, which is a glandular part originated from the oral, ectoderm. ii) Neurohypophysis, which is a nervous part originated from the infundibular region of the brain.
The size of sexually mature platy-fish has a mean anterior posterior length of 472.9 micra, with mean width of 178 micra and mean depth of 360 micra. In platybasic form (Eel), the neurohypophysis consists of flat floor of the caudal infundibulum which sends processes into disc-shaped adenohypophysis. Second which directly regulates the specific enzymatic reactions in the various body cells or tissues.
Thyrotropin hormone is secreted from pro-adenohypophysis (rostral pars distalis) and stimulate activity of thyroid hormones. It is secreted by ACTH cells located between the rostral pars distalis and the neurohypophysis. Secretion of ACTH from pituitary is stimulated by the hypothalamus through corticotrophin releasing factor (CRF).
In some fishes like mummichog (Fundulus heteroclitus), prolactin along with the intermedin enhances the laying down of melanin in the melanophores of the skin. It is evident that the GH secretion may be influenced by osmotic pressure, as release of GH from cultured Salmo gairdneri and Anguilla Anguilla pituitaries greater in a. Pars intermedia of teleost pituitary comprise two kinds of secretory cells, which can be identified by their staining properties.
However, other teleosts such as Carassius auratus, and Gillichthys mirabilis have direct innervation from neurosecretory axons. In fishes the neurohypophysis secretes two hormones, i.e., oxytocin and vasopressin, which are stored in hypothalmic neurosecretory cells. Vasopressin and antidiuretic (ADH) hormones are responsible for the constriction of blood vessels in mammals and thus.
