Cell Structure and Metabolic Regulation 21 



innermost reaches of the cytoplasmic matrix. On this basis, 

 perhaps the mitochondria are not so far removed from the 

 compounds of the blood, including oxygen, as was formerly 

 thought. On the other hand, there is good reason to believe 



-^ 



secretory ^/--^ 



granules ^^ 



Fig. 7. Stylized representation of a cell. Description given in text. 



that the extensive system of intraluminal spaces in some 

 cells can act as a secretory device where, finally, the contents 

 within these spaces are secreted into ducts or into the blood 

 by a process of fusion of the membranes of the ER with 

 the membrane lining the cell. The close disposition of the 



