Looking at the bones of the animals that you eat, it has been quite easy to picture your own bones. From pictures in books and on the Internet, you have also been shown how a human bone looks. You know that it basically has a pearly white color and a smooth surface like that of a marble. In actual though, your bones have more inside it than being that white thing.
There are different layers inside your bones. The hard and outermost layer is called the periosteum. This part of your bone is the most sensitive to external pressures. It contains within it various blood vessels and veins that transport blood and nutrients to be used by the different parts of your body.
After the hard layer of periosteum, the next is the compact bone. The tissue inside the compact bone has very little gaps or spaces thus making it only 5% to 30% porous. It is mostly responsible for giving your bones their common attributes of being white, smooth and strong. In an adult skeleton, 80% of the total bone mass is attributed to the compact bone.
Under the layer of compact bone is the trabecular or cancellous bone. 20% of the total bone mass in your skeleton is attributed to this layer of your bones. It is found mostly in the interior part of your bone and resembles a sponge in terms of physical appearance. As such, it is relatively softer than the compact bone, 30% to 90% porous and with generous amounts of space for the marrow.
Finally, you have the marrow in the innermost part. In terms of physical appearance, it can be likened to a jelly with either a red or yellow hue. The bone marrow is a popular layer because of its important function of producing new blood cells for your body.
Aside from the layers of the bones, there are of course cells within it. There are several types of these cells. One is the osteoblasts, located on the surface of the osteoid seams. They produce a type of protein that manufactures bones and produces hormones. Another type of cell within your bones is the osteocytes. Their main functions include the formation and maintenance of your bone matrix as well as the regulation of the way your bones cope with stress. Lastly, you have the osteoclasts that are mainly responsible for the breaking down of the old bone to be replaced by a new one.