The pituitary gland, also called the’ hypophysis, is a small unpaired rounded body about the size of a large pea weighing approximately 5 g.
It has been called the “master” gland because of the multiplicity of its functions, and because it controls many of the other endocrine glands.
It is found at the base of brain, specifically the diencephalon and is lodged in a depression of the sphenoid bone of the skull called sella turcica, (L. sella, saddle; turcica, Turkish) just at the back of the optic chiasma.
Thus the pituitary is one of the best protected and inaccessible endocrine glands. It is connected with the brain by means of a short, thin stalk, the infundibulum.
It is composed of three lobes ; anterior lobe, intermediate lobe (pars intermedia) and a posterior lobe which differ from one another embryo- logically, histologically, and functionally.
The anterior lobe and the intermediate lobe of the pituitary are known together as the adeno- hypophysis, while the posterior one is known as neurohypophysis.
It has a dual origin embryologically, the anterior lobe and the intermediate lobe arise from a diverticulum of the roof of the embryonic buccal cavity known as Rathke’s poucb, while the posterior lobe arises from an outgrowth of the embryonic brain, specifically the diencephalon.
During embryogeny the two sources of tissue fuse forming the complete gland.
During fusion the anterior lobe along with intermediate lobe becomes pinched off from the roof of the buccal cavity, while the posterior lobe remains permanently attached to the hypothalamus of the brain with a short connection, the infundibulum.
Through this connection the endocrine system retains a vital interdependence with the nervous system.
In the young human the intermediate lobe is a distinct structure but it gradually fuses with posterior lobe and becomes obscured. However, in most vertebrates the intermediate lobe remains as a distinct structure.