Noriaki Ono, D.D.S., Ph.D., Assistant Professor of Orthodontics and Pediatric Dentistry, University of Michigan School of Dentistry

Long bones, like the ones in our arms and legs, grow from their ends. The cobblestone area in the center of this image is a specialized region called the growth plate, which is essential for bone growth. The growth plate is composed of distinct rows of dividing cells called chondrocytes. The red cells are actually labeled clones of cells that originally arose from the same mother cell (the rounder red cells at the top). These perfect rows of clonal cells illustrate the longitudinal direction of bone growth. The rows of chondrocytes first proliferate, then slowly die toward the bottom of the row. Once they die, osteoblasts enter and turn the matrix into bone. This process continues throughout childhood and adolescence, but by about age 20, this growth plate disappears and bones stop elongating.

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