Bony Targets of Non-"skeletal" Hormones 217 



been carried with respect to skeletal physiology. While little material of this sort has 

 been available the situation should be very different after this session. 



The first step needed to develop these concepts is to review the anatomy and 

 physiology of a cell in order to identify potential sites for hormone action. To this 

 end the chief physiological systems of a bone cell have been drawn schematically in 

 Fig. 1. Clearly this is a biochemist's cell, since all the processes carried on by a variety 

 of bone cell types have been confined inside a single cell wall! However, despite the 

 obvious violation of anatomical truth, this diagram can serve to illustrate the im- 

 portant points. 



BONE CELL 



LACTATE CC^ CITRATE 0, 



Fig. 1. A biochemist's view of a bone cell (see text for details) 



Three general schemes of metabolism are shown which represent the 3 major func- 

 tions of bone cells: a scheme for the biosynthesis, storage, and release of a structural 

 protein, collagen, which is, of course, the matrix upon which the mineral phase is 

 ultimately deposited (Glimcher, 1960); a scheme illustrating the biosynthesis, storage 

 and release of an enzyme, collagenase, which is specifically required for the resorp- 

 tion of bone matrix (Nichols, 1963; Woods and Nichols, 1963; Woods and 

 Nichols, in press); and a scheme representing the systems which produce the 

 chemical energy to drive these processes (Borle et al., 1960). Although these represent 

 only a fraction of the metabolic paths present they are sufficient to remind us of the 

 major features of the systems available for hormonal control. 



All 3 begin with the transfer of substrates across the cell membrane. This can 

 occur by diffusion, illustrated by the passage of Oo ; by transport, which, when 

 requiring energy, leads to intracellular concentration of substrates as shown here for 

 glucose and amino-acids (Flanagan and Nichols, unpublished studies) or by the 

 process of pinocytosis. Similar membrane transfer systems, responsible for main- 

 tenance of normal intracellular concentrations of salts and water, have been omitted 

 for simplicity. 



