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Figure 4. In post-menopausal osteoporosis, the decrease of estrogen will lead to increased numbers of osteoclasts and, thus, enhanced numbers of bone multi-cellular units (A). As a consequence, the urinary excretion of calcium and collagen degradation products, such as deoxypyridinoline crosslinks, will be increased. Since more bone multi-cellular units are present in the skeleton of a post-menopausal woman, the number of active osteoblasts will be enhanced, and because of that, the serum level of osteocalcin will be increased (B). The more severe the osteoporosis, the more bone multi-cellular units will be present, and therefore the number of active osteoblasts and serum osteocalcin levels will be an indicator of "high turnover" osteoporosis. However, since the individual osteoblasts are less-well-functioning because of the lack of estrogen, the net effect of resorption and bone formation will be such that the amount of bone tissue will decrease.
