Anatomy and physiology of skeletal tissue: The bone cells

The skeleton is a hard structure formed by a set of bones that support the human body. According to their shape, the bones can be classified into four groups: long bones, short bones, flat bones, and irregular bones. Long bones, the major bones of limbs, are longer than they are wide and consist of an elongated central hollow shaft, known as diaphysis, and two expanded ends, known as epiphysis. The part between the diaphysis and the epiphysis is called metaphysis. The inner portion of the bone includes a cavity, known as marrow or medullary cavity, filled with bone marrow. Short bones are almost equivalent in length and diameter (i.e., the carpal bones of the hand); flat bones are skinny and plate-like (i.e., the skull and the sternum); irregular bones have a different shape with respect to the previously described three groups of bones (i.e., a vertebra).