Sex XXXX and the construction and conservation of the adult skeleton.

@entity172 @entity1 @entity251 @entity73 @entity604 @entity170 @entity442 @entity3528 @entity460 @entity230
Here we review and extend a new unitary model for the pathophysiology of @entity170 that identifies @entity172 (E) as the key hormone for maintaining bone mass and E deficiency as the major cause of age-related @entity604 in both sexes. Also, both E and @entity251 (T) are key regulators of skeletal growth and maturation, and E, together with GH and @entity442 , initiate a 3- to 4-yr pubertal growth spurt that doubles skeletal mass. Although E is required for the attainment of maximal peak bone mass in both sexes, the additional action of T on stimulating periosteal apposition accounts for the larger size and thicker cortices of the adult male skeleton. Aging @entity1 undergo two phases of @entity604 , whereas aging @entity1 undergo only one. In @entity1 , the menopause initiates an accelerated phase of predominantly cancellous @entity604 that declines rapidly over 4-8 yr to become asymptotic with a subsequent slow phase that continues indefinitely. The accelerated phase results from the loss of the direct restraining effects of E on bone turnover, an action mediated by E receptors in both osteoblasts and osteoclasts. In the ensuing slow phase, the rate of cancellous @entity604 is reduced, but the rate of cortical @entity604 is unchanged or increased. This phase is mediated largely by @entity3528 that results from the loss of E actions on extraskeletal @entity460 metabolism. The resultant external @entity460 losses increase the level of dietary @entity460 intake that is required to maintain bone balance. @entity73 due to E deficiency, aging, or both also contributes to the slow phase of @entity604 . Although both serum bioavailable (Bio) E and Bio T decline in aging @entity1 , Bio E is the major predictor of their @entity604 . Thus, both sex @entity230 are important for developing peak bone mass, but E deficiency is the major determinant of age-related @entity604 in both sexes.
