Coloured scanning electron micrograph (SEM) of an osteoclast cell grown in a culture containing calcium-carbonate. Osteoclasts are large, multi-nucleated cells that form from the fusion of several macrophage cells in bone. They are normally present in bones to absorb and remove unwanted bone tissue during normal bone regeneration. In osteoporosis increased activity of the cells contributes to the weakening of the bone and increased risk of fractures. This cell has formed a hole in the calcium-carbonate layer. The picture was created as part of a cooperation with Quintessenz Publishing. Magnification: x2,500 when printed at 15cm wide.