What is bone?
Our fascination with the fossil remains of dinosaurs and other ancient creatures may lead us to believe that bone is a hard, nonliving part of our body and part of the bodies of other animals, including those from long ago. Although bone is indeed solid and strong, allowing form, movement, and organ protection, it is living tissue and constantly changing
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Bone contains several different types of cells, which are supported by a thick fluid called the matrix. Within the matrix reside proteins, primarily collagen, and to a much lesser degree other related substances, such as some really unique carbohydrates. Also in the matrix are mineral deposits, largely a calcium- and phosphate-based crystal called hydroxyapatite, as well as calcium phosphate. |
Bone is roughly 60 to 70 percent mineral complexes and the remaining bone is largely protein (also see Collagen and Hydroxyapatite Figure) primarily collagen. Hydroxyapatite are like tiny, long, and flat sheets of minerals that actually lie on top and along longer collagen fibers. These mineral deposits provide the hard and compression-resisting properties to bone. For the most part, it is also these mineral complexes along with some proteins that exist as fossils long after the death of an animal.
The bone cells (osteoblasts) in the figure above are busy making collagen proteins that form into collagen fibers that are like rope, here in the matrix of bone. Mineral complexes then adhere to the collagen. Collagen makes bone strong and minerals make it hard! In addition to some cells, proteins, carbohydrates, and minerals, other tissue can be found in bone. For instance, small blood vessels run throughout bone and deliver substances to and away from bone. Some nerves can be found in bone as well.
Is bone constantly changing?
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Bone is constantly being turned over. Specific cells within bone are constantly breaking down bone components such as proteins and mineral complexes. Meanwhile, other cells are constantly building bone. Although this may seem counterproductive its merit lies in the ability of bone to adapt or be remodeled according to the demands placed upon it. For example, one of the benefits of weightlifting is an increased stress placed on bone, which causes the bone to adapt by increasing its density. In this case, the efforts of cells that build bone will exceed the efforts of cells that will break down bone components. |
On the contrary, prolonged exposure to zero gravity (weightlessness) in outer space will decrease the stress placed upon bone resulting in a loss of bone density. In this situation, the efforts of cells that break down bone will exceed those efforts of cells that build bone components
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