Time to Pick a Bone

Greetings!

Have you ever broken a bone? Well, count me lucky because fortunately I'm batting 1,000 in that department. No I'm not gloating, but I was just thinking how complex and how vital our bones really are and wanted to remind everyone what bone really is and what an amazing structural component it is in our bodies.

Due to the build up of calcium, bones are very durable and strong.  Bones are our body's foundation, if not for them we would be nothing more than a pile of skin and muscle. They also act to protect us from injury such as falls and impact injuries.  Finally, bones in conjunction with joints (see old blog post) provide movement.

As I had posted earlier in the year, the human body contains 206 bones and are categorized in four types: long, short, flat and sesamoid.  As not all bones are alike, bone structure is not as black and white as you may think. Bone is composed of two layers of tissue that are classified as either compact or trabecular.

Compact bone is actually osseous tissue or the outer layer of the bone, which is the nice white portion of the bone we think about.  Although it looks completely smooth, compact bone actually has many filled with many canals (see figure above)  that allow for blood and nerves to move through. Compact bone also makes up roughly 80% bone in our bodies.  Compact bone is made of special cells called osteocytes. These cells are lined up in rings around the canals. Together, a canal and the osteocytes that surround it are called osteons.(1)

Trabecular bone, often referred to as spongy bone, is the inside layer of the bone and like it's name suggests, is very porous.  Don't be fooled by it's name, spongy bone is quite hard.  The open spaces make room for bone marrow, nerves and blood vessels, which is how nutrients pass through. (1)


Bones are composed of four types of cells:  osteoblasts, osteoclasts, osteocytes, and lining cells.

Osteoblast

Osteoblasts are the cells that make new bones and rebuild bone when we break them.  When there is damage to a bone, many of these osteoblasts come together forming a material called osteoid (2) This is like a foundation, which minerals are then added to bit by bit until the new bone is compete. Once this process is finished they become lining cells or osteocytes. (1)

Osteocyte

Osteocytes, as mentioned above, are the remnants of osteoblasts.  They pile upon each other and with their star like arms, connect with other osteocytes serving as a network, delivering minerals to other cells in the area they are located at. (1)

Lining Cell

Lining Cells are also the bi-product of osteoblasts, but unlike osteocytes the cover the surface of the bone.  Lining cells serve to aid in the movement of molecules in and out of the bone. (2)

Osteoclast

Osteoclasts break down and reabsorb existing bone. Osteoclasts and osteoblasts both aid in the process of reshaping bones. When the bone breaks, callus forms to begin the process of healing and is broken down by osteoclasts until the bone returns to it's original shape.(1) It is also thought that, when new blood vessels, nerves, and veins are needed in an area, osteoclasts break down bone material to make new passages (2). Finally, bones that are used more often and need to support more weight, such as the bones of athletes, become thicker and stronger over time. Bones that are used less often, such as those that need to be put into a cast for long periods of time, are broken down, becoming smaller and thinner. (2)



As you can see from this brief post (it would take many posts to fully understand bones) bone is quite complex and fascinating.  With so many bones in the body, not too mention the joints the create, it's hard not to really appreciate what they do for us on a daily basis.  I hope it never happens to you, but if you or anyone you know breaks a bone, you now know a little knowledge of the rebuilding process a few basic anatomical properties as well. In addition, I'v e included a few models of the Osteogenesis process and how some of these little guys we talked above work as a team.

Thanks for reading!

Another Dream that failed. There's nothing sadder- Captain James T. Kirk


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References

1. Fox, S.I. (2004) The Study of Body Function, Human Physiology 8th Edition (16-18). NY: Martin J. Lange

2. ASU School of Life Sciences (n.d.) Busy Bones. http://askabiologist.asu.edu/bone-anatomy. Retrieved February 13, 2013.


*I am not a doctor or a licensed physician.  I am in no way diagnosing anything and recommend that you speak to your physician before making any medical decisions.

*I am not a registered nutritionist or dietitian. The information presented is for education purposes only.