Brown Adipose Tissue in f/ic Rai 



183 



b 





Fig. 1. Part of a normal brown fat cell. Mitochondria mostly have regular cristac some ot" which are beaded (B). Inter- 

 cristal sections account for the appearance of such bodies as (A). Some mitochondria have vesicular internal membranes 

 at one pole (V) and tiny vesicles are sometimes seen between the cristae (C). Lipid droplets lie freely in the cytoplasm and 

 often interconnect. Endoplasmic reticular elements include a saccular component (S): the granular component (G) 

 occurs independently, and in association with the saccular component. Magnification 61,000. 



The mitochondria are not markedly pleomorphic: 

 although found anywhere in the cytoplasm they are 

 commonly clustered around lipid droplets. From 

 direct measurements their average cross-sectional 

 diameter was calculated as 0.86 //. in some parts of 

 its extent the mitochondrial enclosing membrane 

 may be deficient, and often at points of contact with 

 lipid droplets (fig. 3): osmiophile material may 

 extend between droplet and mitochondrion at such 

 a breach. Mitochondrial internal membranes consist 

 for the most part of double membranes arranged in 



parallel cristae of varying length (tig. 1 ) but vesicular 

 components (figs. 1 and 2) may be admixed with 

 the cristae or concentrated towards one pole as 

 observed in the parathyroid mitochondria (9). The 

 intercristal distance may range from 250 to 850 A 

 throughout the tissue, with a narrower variation 

 within individual mitochondria. The thickness of the 

 cristae (double membrane plus contained space) 

 shows a sitnilar individual and general variation 

 between 150 350 A. The broadest cristae are usually 

 most widely separated and are frequently beaded 



Fig. 2. The mitochondrion (A) contains both cristae and 

 vesicles. The body (B) contains intensely osmiophile vesicles 

 and is intermediate in appearance between the mitochondrion 

 (A) and the lipid droplet (L). Note vesicular components in 

 lipid droplet (see fig. 4). Magnification 47,000. 



Fig. 3. The mitochondrion shown is freely open to lipid 

 drops along the line A-A and at B. Magnification 47,000. 



