Osteoporosis. Coloured scanning electron micrograph (SEM) of osteoporotic bone. Part of the surface of the bone (orange) has degraded, showing the underlying tissue (yellow). This is due to an imbalance in the activity of osteoclasts (cells that reabsorb bone tissue) and osteoblasts (cells that form new bone tissue). Osteoporosis (brittle bone disease) causes a loss of bone mass and an increase in the bone's porosity, making it more brittle and likely to fracture. It commonly affects post-menopausal women, who experience a decrease in levels of the hormone oestrogen. It may also develop after injury or infection. Treatment is with hormone replacement therapy (HRT) and drugs that slow the rate of bone loss. Magnification: x27 when printed 10cm wide.