By Janet Rae-Dupree, Pat DuPree

Human osteology, from the Greek word for “bone” (osteon) and the suffix –logy, which means “to study,” focuses on the 206 bones in the adult body endoskeleton. But osteology is more than just bones; it’s also ligaments and cartilage and the joints that make the whole assembly useful. The skeletal system as a whole serves five key functions:

  • Protection: The skeleton encases and shields delicate internal organs that might otherwise be damaged during motion or crushed by the weight of the body itself. For example, the skull’s cranium houses the brain, and the ribs and sternum of the thoracic cage protect organs in the thoracic body cavity.

  • Movement: By providing anchor sites and a scaffold against which muscles can contract, the skeleton makes motion possible. The bones act as levers, the joints are the fulcrums, and the muscles apply the force. For instance, when the biceps muscle contracts, the radius and ulna bones of the forearm are lifted toward the humerus bone of the upper arm.

    [Credit: ©iStockphoto.com/angelhell]
    Credit: ©iStockphoto.com/angelhell
  • Support: The vertebral column’s curvatures play a key role in supporting the entire body’s weight, as do the arches formed by the bones of the feet. Upper body support flows from the clavicle, or collarbone, which is the only bone that attaches the upper extremities to the axial skeleton and the only horizontal long bone in the human body.

  • Mineral storage: Calcium, phosphorous, and other minerals like magnesium must be maintained in the bloodstream at a constant level, so they’re “banked” in the bones in case the dietary intake of those minerals drops. The bones’ mineral content is constantly renewed, refreshing entirely about every nine months. A 35 percent decrease in blood calcium will cause convulsions.

  • Blood cell formation: Called hemopoiesis or hematopoiesis, most blood cell formation takes place within the red marrow inside the ends of long bones as well as within the vertebrae, ribs, sternum, and cranial bones. Marrow produces three types of blood cells: erythrocytes (red cells), leukocytes (white cells), and thrombocytes (platelets).

    Most of these are formed in red bone marrow, although some types of white blood cells are produced in fat-rich yellow bone marrow. At birth, all bone marrow is red. With age, it converts to the yellow type. In cases of severe blood loss, the body can convert yellow marrow back to red marrow in order to increase blood cell production.