There are two divisions of the human skeleton: axial and appendicular. The skeletal system helps provide support, protection, movement, mineral (and lipid) storage and areas (marrow_cavities) where blood cell formation occurs. Each bone in the skeletal system has a unique shape, size and surface markings.

The structure of a typical long bone includes the diaphyses (sing: diaphysis), epiphyses (sing: epiphysis), epiphyseal_lines, articular_cartilages, periosteum, endosteum, yellow_marrow (medullary) cavity, red_marrow (medullary) cavity, Sharpeys_fibers, nutrient_foramen, and nutrient_arteries.

The diaphysis forms the long axis of the bone and is often called the shaft of the bone. The epiphyses are the ends of the bone, and are usually significantly wider than the diaphysis. Adults have epiphyseal lines that mark the junction of each epiphysis with the diaphysis. These lines represent the remains of the epiphyseal_plate (growth plate) of childhood. The surface of each epiphysis is covered with articular cartilage (composed of hyaline_cartilage), which helps protect the ends of the bone at their articulation points.

The outer surface of the bone is covered with the periosteum and the cavity of the bone is lined by the endosteum. Both these membranes are sites of osteoblast and osteoclast activity. Blood vessels, nerves and lymphatic vessels enter the bone via the nutrient foramen, an opening associated with the periosteum. Sharpeys fibers help secure the periosteum to the outer surface of the bone. Red marrow cavities within these bones are sites of blood cell formation and yellow marrow cavities are used for lipid storage.