Background

The skeletal system is the primary structural organ system of the body. Many people think of the skeletal system as being static in that it is unchanging, however, this is not the case. Bones, like other organ systems, have specialized cells which allow them to perform a variety of essential tasks. Osteoblast are responsible for secreting the bony matrix necessary for bone formation. Osteoclast, meanwhile, are large multinucleated cells responsible for the dissolution and reabsorption of bone.  It is made mostly of collagen, which gives bone its soft framework, and calcium phosphate which adds strength and hardness to the structure. It is divided into the axial and the appendicular skeleton. The axial skeleton consists of the skull, hyoid bone, vertebral column, sternum, and ribs. Whereas the appendicular skeleton consists of the clavicle, scapula and the rest of the upper and lower limbs. Without the foundational structure of the skeletal system, there would be nothing to support the body and provide points of attachment for muscles. Bones function to protect internal organs, assist body movements, store and release calcium and phosphorous, participate in blood cell production and store fat in the yellow marrow. Bones also function to protect internal organs, assist body movements, and the storage and release of ions such as calcium and phosphorous. Furthermore, long bones contain both hemopoietic (red) and stromal (yellow) marrow which produce red blood cells and fat cells respectively.  Each of these cells have specific functions that are key to the development and repair of a bone over time. The two types of bone tissue are compact and spongy bone. Compact bone is typically found along the perimeter of bones and makes up the majority of the diaphysis of long bones. It is stronger than spongy bone and provides more stability. Compact bone is made up of circular units called osteons. Osteons are composed of rings called lamellae that spiral down into a central canal, known as the Haversian canal. This central canal is the passage for nerves, blood vessels, and lymphatics. Spongy bone, on the other hand, is typically the deepest layer of a bone’s composition. It is made of trabeculae which give spongy bone its characteristic lighter weight. There are five classifications of bones based on their shape, long bones, short bones, flat bones, irregular bones and sesamoid bones. The shape and composition of each bone allow them to function as mentioned above.

Vocabulary for Bones and Bone Markings on page(s) 161-162.