Despite appearing extremely sturdy human bones actually have a measure of flexibility, allowing protection against jarring falls. Bones are also responsible for supplying the body with the majority of its blood supply.
Bones are Made of Living Tissue
Bones are made up of living tissues in addition to protein, mineral salts and water. There are two types of cells that make up the majority of the bone: osteoblasts and osteoclasts. Osteoblasts are the cells responsible for building new bone and osteoclasts are responsible for breaking it down. These cells are constantly working to rebuild bones, keeping them in a constant state of renewal. Keeping this state up minimizes the general wear and tear our bones face every day.
Basic Bone Structure
Every bone, whether big or small, has an outer layer of compact bone. Compact bone is dense tissue made up of osteons arranged in rings. The rings have white spots at the center which allow for blood vessels and nerves to travel through. Inside the compact bone is a lighter spongier layer of bone. The spongy layer has a honeycomb appearance and keeps the skeleton from being overly heavy. Bone marrow is located within the spongy layer. Between the layers there are tiny spaces for bone cells and fluid to provide nutrients to the bone.
Bone Development and Growth
In a fetus the growing bones are made of tough, springy cartilage, by the time that the baby is born that cartilage has hardened into bone. The process of cartilage into bone is known as ossification. In newborns the shaft of the bone is completely hardened but the ends of the bones are still cartilage. Between the shaft and the end of the bone is the growth plate, which produces more cartilage to elongate the bongs as the child grows. That cartilage goes through ossification. The process continues until the age of about eighteen. Once the body has reached adulthood the growth process and ossification is complete and the ends of the bones have become hard bone.
Bone Repair
Bones have an amazing ability to repair themselves after injuries such as fractures or breaks. Once a bone breaks a blot clot begins to form and then the bone cells immediately begin to form new spongy tissue. It usually takes a fracture, such as in the leg or arm, about 6 weeks to repair itself. In children, whose bones are still growing, it usually takes less time to heal. Bones need to be immobilized so that they will eventually regain their former shape.
Bones' amazing ability to grow and constantly repair themselves come from their structure and the cells they are made up of. The way that bones are made allows for the strength to hold our bodies upright while be flexible enough to absorb the shocks of everyday life. In addition to provide the human body with a basic support system bones provide a major source of blood for the human body.
Source: Tortora, Gerard and Sandra Grabowski. Principles of Anatomy and Physiology, 10th Edition. Wiley, New York. 15 June 2002.
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