The ultrastructure of bone.

The ultrastructure of the three specialized bone cells are described in relation to their function. Osteoblasts are the bone forming cells with an abundance of RER and a large Golgi area. Osteoblasts and osteocytes form an integrated cell system connected with each other by cell processes filled with actin-like filaments and joined by specialized cell junctions, probably gap junctions. Osteoclasts resorb bone. Characteristics are multiple nuclei, and abundance of mitochondria, a sparcity of RER and clusters of ribosomes. Lysosomes and vesicles contain hydrolytic enzymes. The resorbing area consists of a ruffled border completely encircled by a clear zone.