ASTRID & HANNS-FRIDER MICHLER / SCIENCE PHOTO LIBRARY ASTRID & HANNS-FRIDER MICHLER / SCIENCE PHOTO LIBRARY
Light micrograph of normal human cartilage at the surface of an articulated bone joint. Cartilage consists of cells, called chondrocytes, seen here as dark purple, which secrete a matrix of collagen fibres and acidic polysaccharides. The retention of a cartilage layer at the surface of the joint bones enables the joint to move smoothly. In this picture the orange region represents calcified bone material. The surface of the joint is to the top of the picture; in reality the empty space shown above the cartilage would be filled with synovial fluid to lubricate the joint. Magnification: x20 at 35mm size.
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