CELL I LTR ASTRUCTl RE IN >IA>L>IALS 



Fig. 16. Hydroxyapatite crystals, located in a concretion, experimentally pro- 

 duced in the tubular lumen of the proximal convolution of the rat kidney by injecting 

 subcutaneoush" large doses of parathyroid hormone. (From Engfeldt, et al., 1958). 

 Magnification 16o,000X 



grate toward the luminal part of the cell Mucous secretion. In secretory cells with a 



where, in some instances, it can be seen that production of mucin, the secretory granules 



the limiting membrane of the granule fuses are not bound by a membrane. Frequenth', 



with the surface plasma membrane and the fusion of several mucous granules occurs, 



granule empties its content into the lumen, and the discharge of mucin does not occur 



111 



