Physiology of Finfish and Shellfish (2+1)

5.2.2.2.1. Anatomy of pituitary gland - Anterior pituitary (Adenohypophysis)

This is made of 3 parts called the rostral pars distalis, proximal pars distalis and the pars intermedia.

a. Rostral pars distalis

Rostral pars distalis is the anterior most part of the adenohypophysis and is composed of acidophilic cells. These cells are stained by azocarmine or orange G stains. Along with the acidophils, a few cyanophils are also present. These cells are stained by aniline blue, aldehyde fuchsin (AF) and aldehyde thionine stain. A few non granular cells that do not take any stain, may also be present and are called chromophobes.

b. proximal pars distalis

It lies between the rostral pars distalis and the pars intermedia. This contains acidophils, cyanophils and chromophobes cells and may vary in size during different parts of the year. During maturation and spawning periods, the cyanophils are more numerous than the others but during the rest of the year the acidophils are larger in number. The acidophilic cells are of 2 types called erythrosinophilic and orangeophilic cells and can be stained with azocarmine or orange G stains. The cyanophils are the principal type of cell in the proximal pars distalis and can be further differentiated into 2 categories on the basis of shape, size and staining affinity. These are stained with aniline blue, PAS and AF stains. The chromophobes do not take any stain.

c. The pars intermedia

It is the posterior part of the hypophysis and may be of various sizes in different species. It consists of 2 cell types.

1. Cyanophils that are stained with aniline blue
2. Acidophils that can be stained with azocarmine or orange G.

In some species amphilic cells are also present which stain by both aniline blue and orange stain. A few chromophobes may also be present. The cyanophils are negative to PAS, aldehyde fuschin and aldehyde thionin stain. When pituitary is stained with PAS followed by lead haemotoxylin (PbH), 2 distinct cell types are observed in some species. PAS- +ve cells are oval in shape and are situated near the border of the neurohypophysis, while the second type of cells is stained with lead haemotoxylin. Pars intermedia are well vascularised and are believed to secrete 2 distinct hormones.