The pituitary cells are regulated by numerous endocrine, paracrine and autocrine feed-back pathways, and their hormone secretion exerts major control over the function of several endocrine glands as well as a wide range of physiologic states. During estrus STH cells are spherical to oval in shape with the spherical nucleus. Cytoplasm of STH cell is filled with a large number of round to oval shaped secretory granules of diameter ranges from 200-400nm. STH cells during early pregnancy are polyhedral in shape with eccentric nucleus and mostly euchromatic. Mitochondria are spherical to oval in shape with lamellar cristae. The Golgi zone is observed juxtanuclear in position. Secretory granules are increases in number as compared to estrus. STH cell during lactation are polyhedral in shape. Rough endoplasmic reticulums are elongated, tubular dotted with ribosomes. Secretory granules are seen scattered in the cytoplasm. The diameter of secretory granules is about 230 nm.