Bone

Bone is the substance that forms part of the endoskeleton of vertebrates. It is composed chiefly of calcium phosphate and calcium carbonate. There are 206 bones in the adult human body and about 270 in an infant. They provide support and movement, and protect the various organs of the body, produce red and white blood cells and store minerals.

Bone Anatomy

Types of Bones

There are generally five categories of bones: long bones, short bones, flat bones, irregular bones, and sesamoid bones. Long bones are longer than they are wide and work as levers. The bones of the upper and lower extremities (ex. humerus, tibia, femur, ulna, metacarpals, etc.) are of this type. Short bones are short, cube-shaped, and found in the wrists and ankles. Flat bones have broad surfaces for protection of organs and attachment of muscles (ex. ribs, cranial bones, bones of shoulder girdle). Irregular bones are all others that do not fall into the previous categories, with the exception of sesamoid bones (see below). Irregular bones have varied shapes, sizes, and surfaces features and include the bones of the vertebrae and a few in the skull.

long bones

Long bones are longer than they are wide (femur).

short bones

Short bones are shaped like cubes and are found primarily in the wrist and ankles.

flat bones

Flat bones are thin, flat, and curved; they form the ribs, breastbone, and skull.

irregular bones

Irregular bones are different shaped and are not classified as long, short, or flat; they include the hip bones, vertebrae, and various bones in the skull.

sesamoid bones

Sesamoid bones are small round bony masses embedded in certain tendons that may be subjected to compression and tension; the largest sesamoid bone is the patella, which is embedded in the tendon of the quadriceps femoris at the knee.