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.

Bone contains several different types of cells, which are supported by a thick fluid called the matrix. As oversimplified in Figure 2.3, 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 phosphatebased crystal called hydroxyapatite, as well as calcium phosphate. Bone is roughly 60 to 70 percent mineral complexes and the remainder is largely protein (also see Figure 10.1), primarily collagen. Hydroxyapatites 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.
 

Bone is composed of minerals such as calcium, phosphate, and magnesium and protein such as collagen.
 

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.