Bone tissue: composition and function.

A relatively small amount of bone tissue is present in the human body in view of the tissue's structural and chemical importance. The disparity between the constant appearance of mineralized bone matrix, regardless of source, under the electron microscope and the variability of previously reported analyses of bone specimens of a much larger size was disturbing and led to studies of the content and distribution of water in bone tissue and in whole bone specimens. Water in premineralized bone matrix is largely replaced by the non-crystalline (amorphous) and crystalline mineral phase without changes in the overall volume of bone matrix or that of whole bones, nor in the volume and position of collagen fibrils. This resistance to volume and fibril position change during mineralization is probably unique to bone tissue, and permitted critical water analyses of whole bone specimens of varying porosity. When marrow and bone tissue weight and volume analyses were compared with the specific gravity of whole bone specimens, constancy of the composition of bone tissue in these specimens was demonstrated. This result led to a concentration of our studies on the cells that synthesize and control this unique tissue. Currently, the investigations of this laboratory are oriented to study of the enzyme chemistry of isolated bone cells and of whole bone specimens, as well as the localization of matrix-bound and membrane-bound enzymes in bone tissue by histochemical techniques suitable for electron microscopy.