Anatomy of finfish and shellfish

Unit 9 - Endocrine system

9.2. Pituitary gland
The arrangement and organizations of the component parts of pituitary gland varies greatly in different species.Olivereace,1954,has recently discussed the terminology and the homologus of the different area.the pituitary gland or the hypophysis develops from two parts as follows:

• Neurohypophysis derived from the brain.
• Adenohypophysis which develops as an ectodermal up-growth the roof of the buccal cavity (Rathke’s pouch).

The Hypophysis of the ventral side of the brain just behind the optic chaisma and is attached to the infundibulam by means of stalk.In some fishes the stalk is absent and the gland is pressed closely against the floor of the brain.
Adenohyphophysis
The adenohypophysis is divided into pars distallis and pars intermedia. Of these the parsis further divided into rostral pars distalis (Pro-adenohypophysis)and posterior distalis (meso adenohyphophysis).the pars intermedia corresponds to the meta adenohypophysis of the older terminology.
Neurohypophysis
The region consists of a large number of nerve fibres that arises from cells bodies in the hypothalamus and enter the hyphophysis,where they branch repeatedly and ramify in the pairs intermedia.
Pituitary in Elasmobranch
The neurohypophysis of this group is diffused and intermingled with the pars intermedia.the two parts are often been collectively referred to as neurointermediate lobe.Neurosecretory axons are arose from the paraoptic nuclei and lateral hypothalamus terminate in the neurohypophysis but,these are absent from the anterior infaundibulam floor.a few such fibres termed the saccus vasculosus are folded and highly vascularised structure laying posterior to the neurohypophysis. The pars distalis lies below the infandibulam and is divisible in the procentral and rostral zone.the ventral lobe is a peculiar feature of the Elasmobranches adenohypophysis and varies greatly in size and shape among different species.