The Ultrastructure of the Thyroid Gland of the Mouse 



R. Ekholm and F. S. Sjostrand 



The Laboratory for Biological I'ltrastriictiirc Research of the Departnicm o/ Anuioiiiy. hciro/iiiskci hi.sririiict, Stockholm, 



ami the Department of Anatomy, University of Gothenburg 



This paper presents the results obtained mainly by 

 studying the thyroid gland of mice kept in normal 

 laboratory conditions. These results will be the basis 

 of a further analysis of the structural changes in the 

 thyroid in connection with the stimulating and 

 inactivating of the gland. 



The thyroid has earlier been studied with aid of 

 the electron microscope by several investigators (1,2, 

 4). The observations made by these authors are in 

 general accord. Thus, they all give an account of the 

 existence of microvilli on the follicular surface of 

 the thyroid cells and a "lamellar"" or "canalicular"" 

 structure in the cytoplasm. However, as regards the 

 structure of the capillaries, opinions are at variance. 

 Monroe suggests that, in places, the endothelium 

 lining of the capillaries is discontinuous but Demp- 

 sey and Peterson are of the opinion that close exa- 

 mination always reveals a continuous capillary wall. 



Material and methods. — The thyroid gland of 40 adult 

 white mice were examined. The fixation of the tissue 



specimens was performed in a blood isolon 1 per cent 

 osmium tetroxide soliilion, butVered at pH 7.2 with 

 veronal acetate, a modification of the osmium solution 

 of Palade (6). The specimens were embedded in a mixture 

 of /;-biityl and /;-methyl niethacrvlate mainly according 

 to Newman et al. The uluathin sectioning was perft)rmed 

 partly with the microtome designed by Sjostrand (7), 

 partly with an instrument described by Kkholm &Zelan- 

 der (3). The sections were examined partiv in an RCA 

 EMU 2b, partly in an RCA EMU 3b microscope. 



Results. — The thyroid cells are organized accord- 

 ing to a very regular pattern as revealed by a survey 

 picture (tig. I). The cells are bordered by a plasma 

 membrane which at the top surface, facing the follicle, 

 protrudes in a greater or lesser number of microxilli 

 of varying size and shape. At the base the cell 

 membrane, associated with a basement membrane, is 

 usually seen to run in close vicinity to a capillary. 

 The cell nucleus is situated in the centre of the cell. 

 A large number of mitochondria are evenly dis- 

 tributed throughout the cells. The apical zone of the 



Fig. I. Survey picture of mouse thyroid cells with the follicle (uppermost), cell boundary (CB), mitochondria (M). intra- 

 cellular cytoplasmic membranes (CM), nuclei (N) and capillary (C). Magnification 12,000. 



