The Human Skeletal System
The human skeletal system is a multifunctional marvel of biology. It not only provides the framework by which all practical movement is made possible, but protects the organs from injury and bears the weight of your body 24 hours a day. The bones also bank valuable minerals like phosphorous and calcium, and assemble blood cells that carry oxygen and fight disease. Our skeletons start out as small structures, built to support tiny infant babies. As our bodies increase in size and stature, the bones must adapt to fit the change.
Length
Before reaching physical maturity, a person's bones are not fully connected to one another. Throughout your first 20 years, a small space remains between the shaft and joint of each bone, which is filled with a sponge-like material called hyaline cartilage. This region is known as the growth zone. Through division, additional cartilage cells are added to the area, and those new cells then calcify into hard tissue through a process termed ossification. While growing, the bone shaft gradually moves toward the joint. When they connect, growth is complete.
Width
Bones expand in width by secreting cells called osteoblasts from the inside. These cells encase the outer layer of bone, wrapping it in a gel-like material. This material then hardens, eventually becoming bone itself. At the same time osteoclasts, cells that dissolve bone tissue, enlarge the inner cavity by eating away some of the pre-existent bone near the marrow. The result is a bone that has broadened significantly in scope and strength. This operation requires precision and timing. If the inner substance is dissolved too quickly, the bone becomes fragile and brittle. If too much bone is added to the outer layer, the result is abnormal growth or deformation.
Other Bone Transformations
An adult human body contains just over 200 bones. As newborns, however, this number is much larger, totaling approximately 300. This is because several bones that are separate at birth join together later in life. Bone seems to be solid, but is actually laden with microscopic pores that allow blood cells to travel as needed. Cells within the marrow that have the ability to transform into a number of various tissues, metamorphose into the osteoblasts that eventually become calcified bone.
