The human skeletal system is advantageous in the fact that it serves many important functions. However, all of these functions fall within three main categories: the skeleton provides protection, movement, and support; it stores a large quantity of the calcium, fatty tissue, and phosphorous within the body; and it enables other organ systems to function properly.
First of all, the rigid skeleton provides a large amount of protection to the many organs and tissues inside the human coelom. The cranium or skull is a worthy example as it protects and cushions the brain. Also, the rigidity of the skeleton contributes support. The rigid skeleton holds the organs and muscles, allows humans to move against the gravitational pull of the earth, and allows humans to stand and sit. The spine, legs, pelvis, and feet provide most of the support within the body. The rigidity of bone also allows movement. Muscle attachment, in conjunction with joints, permits certain bones to move in a variety of different planes and to function as Class One, Two, or Three levers.
Second, the skeletal system houses most of the body's calcium, fatty tissue, and phosphorous. Although both are stored within the bone matrix, calcium salts are stored as hydroxyapatite, a complex, crystalline molecule. The hydroxyapatite is converted to calcium by osteoclasts during periods in which calcium is needed by the body, and the hydroxyapatite is converted into new bone tissue in times of excess. Fatty tissue is stored in the medullary cavity as yellow bone marrow; the yellow marrow provides the body with energy when the amount of body fat has been reduced.
Lastly, the skeletal system is key the proper function of many of the other organ systems of the body. For example, red bone marrow, which produces erythrocytes, leukocytes, and thrombocytes, which are red blood cells, white blood cells, and platelets, respectively, is the primary source of blood cell production and is essential to the circulatory system although yellow marrow is used to produce erythrocytes in times of anemia. Bones also aid in the respiratory system as the ribs are necessary for the diaphragm to contract, allowing air to enter the lungs. Three small bones, the hammer, anvil, and stirrup of the inner ear, regulate hearing and balance.
In conclusion, the human skeletal system is required for many of the processes that occur within the human body, and it is essential for ultimately maintaining homeostasis and metabolism.