24 The Anatomy of the Salivary Glands 



In the electron microscope mitochondria are found diverse in 

 size, but generally are sausage-shaped bodies with an outer double 

 membrane of the same thickness as the e.r. membranes. The inner 

 membrane may be thrown into complicated folds (cristae mito- 

 chondriales), which increase the available internal surfaces. In the 

 acinar cells the mitochondria are not very numerous (Leeson and 

 Jacoby, 19596; Hill and Bourne, 1954) (but compare Pease (1956), 

 who states: "The basal half or two-thirds of the serous cells is 

 ordinarily so jammed with mitochondria that there is hardly room 

 for other components"). In the striated duct cells mitochondria 

 are much more frequent and are characteristically found packed in 

 parallel rows between the areas of membrane infolding. In no cells 

 up till the present has continuity between mitochondria and any 

 other cell membranes been demonstrated, although Robertson 

 (1959) speculates that these occur and proposes a scheme for for- 

 mation of mitochondria from the plasma membrane. 



Studies with isolated mitochondria have established that these 

 are the major site of cell respiration (for reviews and bibliography 

 see Lindberg and Ernster, 1954; Ernster, 1959) and contain the 

 whole of the cell cytochrome oxidase and the major part of the 

 enzymes of the citric acid cycle. Roughly speaking the density of 

 mitochondria in a cell corresponds to its respiratory activity. 



Secretory granules appear in the resting cell as dense round 

 bodies 0-5-2 // diameter congregated at the cell apex (Siekevitz and 

 Palade, 1956). In this state it is difficult to be certain that they are 

 enclosed in a cytoplasmic membrane, but in the active cell the 

 granules can clearly be seen lying within membrane-lined cavities 

 within which they undergo more or less complete dissolution. 

 These granule-containing cisternae appear to undergo extrusion 

 into the acinar lumen (Fig. 2.8). Granules of this type are seen 

 especially in the granular tubules of the rat submaxillary, less 

 prominently in the acinar cells and are rare in the striated ducts 

 (Leeson and Jacoby, 19596). In the lamb parotid acinar cells gran- 

 ules appear to be scarce (Manni, Grillo and Ambrosino, 1957). A 

 comparison of serous and mucous acinar cells by this technique 

 would be of considerable interest. 



Hokin (1955) isolated zymogen granules from homogenates of 

 dog pancreas in a sucrose medium at pH 5-6. The granules were 

 rich in protein but contained much less phospholipid or RNA than 

 other cell fractions. The granules underwent rapid dissolution 



