BONES HAVE EARS

The movement of bone fluid from the region of the bone vasculature through the canaliculi and the lacunae of the surrounding mineralized tissue accomplishes three important tasks. First it transports nutrients to the osteocytes in the lacunae buried in the mineralized matrix. Second, it carries away the cell waste. Third, the bone fluid exerts a force on the cell process, a force that is large enough for the cell to sense. This is probably the basic mechanotrasduction mechanism in bone, the way in which bone senses the mechanical load to which it is subjected. The mechanism of bone fluid flow are described below with particular emphasis on mechanotransduction. Also described is the cell to cell communication by which higher frequency signals might be transferred, a potential mechanism in bone by which the small whole tissue strain is amplified so the bone cells can respond to it. One of the conclusions is that higher frequency low amplitude strains can maintain bone as effectively as low frequency low amplitude strains can maintain bone as effectively as low frequency high amplitude strains. This mechanism has many similarities with the mechanotransduction of acoustical signals in the ear. These conclusion leads to a paradigm shift in how to treat osteoporosis and how to cope with microgravity.