Functional classification of cell types of the anterior pituitary gland accomplished by electron microscopy.

Light microscopy has revealed that the anterior lobe of the pituitary gland contains many kinds of glandular cells, which have been classified according to the staining behavior of each cell type after the use of various methods of differential staining. At the early stage in the development of pituitary morphology, the cell types were designated as acidophil, basophil or chromophobe suggesting their stainability, or they were called alpha cell, beta cell and so on, implying only the morphological difference between cell types (ROMEIS 1940). Physiology of the anterior pituitary which showed a great progress in recent years indicated six different hormones secreted from this gland. Then many authors attempted to correlate each of these six hormones with one of the various types of glandular cells, as cell types different in morphology from each other were believed to be different in function, too. Such a classification of pituitary cells in view of functional standpoint means the identification of the cellular source of the known anterior pituitary hormones. Each of the three cell types of the anterior lobe, viz, the acidophil, basophil and chromophobe, originally classified by pioneer microscopists was further divided into two or three subtypes as a result of the specific staining techniques of the light microscopic histochemistry, though some of these staining methods were not so widely used (HALMI 1950, DAWSON 1954). Electron microscopy is far more advantageous than light microscopy even with the advanced techniques of histochemistry for morphophysiological studies of the anterior pituitary, because the electron microscope has extremely high resolving