HYPOPHYSEAL MORPHOLOGY 



2L3 



ined by light microscopy. Its use is un- 

 fortunately incompatible with most of the 

 staining techniques on which light micro- 

 scopists have come to rely. For the fixation 

 of tissues for light microscopy, use has been 

 made of a number of fixatives, which permit 

 subsequent staining by various methods, 

 but which do not satisfactorily preserve 

 fine structure even at the level visible by 

 light microscopy. These fixatives cause an 

 extensive redistribution of the proteins of 

 cells during fixation as is shown by an in- 

 crease in opacity and light scattering power 

 during fixation. 



No exact correspondence can be expected 

 between the appearances of structures seen 

 in electron micrographs of osmic acid fixed 

 tissues and of structures rendered visible 

 by staining in tissues fixed by other meth- 

 ods. 



Cytoplasmic structures visible in electron 

 micrographs of adenohypophyseal cells 

 (Figs. 3.25-3.32)1 include the endoplasmic 

 reticulum, the components of the Golgi re- 

 gion, the Palade granules, mitochondria, 

 secretion granules, and lipid droplets. Thus 

 far electron microscopic observations of the 

 pituitary have revealed nothing new with 

 respect to the finer structures of these parts 

 (Palade, 1953), and nothing that is sug- 

 gestive of specific hypophyseal function. On 

 the other hand, only a first step has been 

 taken, but it is expected that further studies 

 will lead to clarification of the many prob- 

 lems to which allusion has been made. 



A. ENDOPLASMIC RETICULUM 



The endoplasmic reticulum is a cavitary 

 system consisting of tubes, vesicles, and 

 flattened sacs interconnected by narrower 



^The electron micrographs of the cells found 

 in the pars anterior and pars intermedia of the 

 rat were contributed by Dr. Marilyn G. Farquhar 

 who also supplied the descriptions. The electron 

 micrographs, which were specially prepared for 

 this publication are, as a result of recent technical 

 advances, of higher quality than those appearing 

 in the original publications. All were prepared 

 from tissues fixed in osmium tetroxide buffered 

 with acetate-veronal buffer to pH 7.4 and em- 

 bedded in n-butyl methacrylate. Sections of 20 to 

 50 m/x were prepared with a Porter-Blum micro- 

 tome (Servall) and examined and photographed 

 in an RCA EMU-2 electron microscope. Further 

 technical methods are detailed elsewhere (Farqu- 

 har, 1956). 



channels to form a complicated network 

 (Palade, 1956). The system is enclosed by 

 a continuous membrane which is probably 

 similar to and derived from the cell mem- 

 brane (Howatson and Ham, 1957). The 

 endoplasmic reticulum varies considerably 

 in extent and form in different cells. When 

 it is extensive the cross-sections of its mem- 

 brane-enclosed cavities may occupy the 

 greater part of the cytoplasm. The mem- 

 branes are not revealed by any staining 

 methods used in light microscopy and the 

 cavity usually contains no stainable con- 

 tent. In consequence light microscopy gives 

 little indication of the existence of the endo- 

 plasmic reticulum. The larger vesicles which 

 form part of the endoplasmic reticulum of 

 the basophil cells of the rat pars anterior 

 are, however, visible in paraffin sections ex- 

 amined by light microscopy and confer on 

 the cytoplasm a foamy appearance which 

 was noted by Reese, Koneff and Wainman 

 in 1943. Under conditions of rapid secretion, 

 hyaline substance accumulates in these 

 vesicles which become much more easily 

 visible by reason of their enlargement and 

 the presence of a stainable content. That 

 hyalinization is an accumulation of a stain- 

 able material in cytoplasmic vesicles which 

 are always present but normally empty 

 was first stated by Reese, Koneff and Wain- 

 man and confirmed by the electron micro- 

 scope studies of Farquhar and Rinehart 

 (1954a, b). Electron microscopy did not 

 therefore provide the first evidence for the 

 existence of the endoplasmic reticulum, but 

 it showed for the first time its full extent, its 

 continuity, and its existence in all types 

 of cells. 



B. THE GOLGI REGION OR ZONE 



The Golgi region or zone has long been 

 a focal point of discussion by investigators 

 of pituitary morphology and function (Sev- 

 eringhaus, 1932, 1933, 1939). In suitable 

 preparations studied by< light microscopy 

 it is often seen as a conspicuous feature of 

 granulated cells in the pars anterior, this 

 specialized region of the cytoplasm being 

 made evident by the absence from it of the 

 granulation which is distributed throughout 

 the remainder of the cytoplasm. In sections 

 which are sufficiently thin, an unstained 

 zone is seen producing an appearance which 



