Functional Classification of Cell Types of the Anterior Pituitary Gland Accomplished by Electron Microscopy

Recent progress in endocrine physiology showed six different hormones secreted from the anterior pituitary gland, but their cellular sources were not completely elucidated, when the morphological technique was confined to the light microscopy. Application of the electron microscope is very advantageous to the field of functional morphology of the pituitary gland. Within a few years, the identification of cellular sources of the six known hormones of the anterior pituitary has been established in the rat and mouse.Methods for determination of endocrine function of each cell type distinguished by electron microscopy are discussed in detail. Some of them have been fully utilized by electron microscopists who are engaged in functional morphology of the anterior pituitary gland, but a few remaining ones are still in the trial stage.The nomenclature of the anterior pituitary cells indicating the morphological characteristics is now replaced by a new terms implying the function, namely indicating the hormone which is secreted by a given cell type.As the rats have been most frequently observed and best known as to function, the description of this paper is concentrated to the rat anterior pituitary. The electron microscopical features of each of the seven cell types in either normal, pathological or experimental condition are described, and some representative electron micrographs are illustrated.