THE PATHOGENESIS OF OSTEOPOROSIS

Consensus and WHO definitions of osteoporosis are provided. The pathog enesis of the disorder has genetic, hormonal and environmental influen ces which affect peak bone mass. perimenopausal bone loss and age-depe ndent bone loss. Peak bone mass is mainly genetically determined, thou gh dietary factors and physical activity can have positive effects. Pe ak bone mass is attained at the point when skeletal growth ceases, aft er which time bone loss starts. Loss of oestrogen with the menopause r esults in accelerated bone loss. Bone remodelling balance tips in favo ur of osteoclastic bone resorption, with osteoblastic bone formation n ot able to match the level of resorption. Hormone replacement therapy can reverse this trend. Proposed mechanisms and the parts played by th e different cell populations and factors are discussed. Osteoblasts ar e particularly sensitive to ageing phenomena - more sensitive than are osteoclasts, so the negative bone balance increases with increasing a ge. Age-dependent bone loss is aggravated by reduced calcium absorptio n, a mutation in the collagen gene and polymorphism in TGF-beta and oe strogen receptor proteins.