In Praise of Bones

Did you know that bone is the only tissue in the body that heals with itself?   If you cut your skin, it heals with scar tissue. If you lacerate your liver, brain, kidney, lung, it heals with scar tissue.  If you fracture a bone, it heals with bone.  It makes sense, doesn`t it?   If the skeleton healed a broken bone with scar, an inferior tissue compared with the original, then it would be at risk for re-fracture at that site, even as we went about our normal activities.   Early man would never have survived, for obvious reasons.

This illustrates one of bone`s important functions:  Support.  Bones support our frame whether we`re sitting, walking, lifting, or running the hundred yard dash.  The bones are our scaffolding to which our muscles attach, propelling us along, flexing and extending at our joints.  Muscles plus bones constitute our Musculoskeletal System.  Orthopedic Surgeons specialize in the care and treatment of problems of this system.

Another bone function is Protection.  The skull protects our brain, our rib cage protects our heart and lungs and our bony spine protects our fragile spinal cord.

A third function, one you might not realize, is Storage.  Our skeleton is a veritable bank of calcium.  Calcium is a critical regulator of many functions in our body.  Some of the more important ones are muscle contraction, blood clotting, and intra cellular health.   Our blood calcium levels are tightly regulated.  When the body needs to increase its blood level of this mineral, it can`t wait until you have a glass of milk, or a cup of yogurt.  When it needs calcium, it needs it now.  One of the key ways it does this is to signal the bones to release calcium through a complicated mechanism involving PTH (parathyroid hormone).  But, just like a bank that expects you to pay back the money you borrow, the bones expect you to replenish what you`ve borrowed by taking in an adequate amount of calcium in your diet.  If the calcium is not replaced, the skeleton runs a deficit, and if this continues, you have a diminished Bone Mineral Density (BMD), which eventually leads to Osteoporosis.  Osteoporosis is worrisome, and we will talk about this condition at some length in a future column.

The last major function of bone is Synthesis.  Bone marrow is a semi liquid substance that resides in the center of our bigger bones, especially the flat bones like the pelvis and sternum. The bone marrow manufactures a variety of cells: red blood cells, which carry oxygen, white blood cells, which are important for immunity, and platelets, essential for blood clotting.  In addition, bone marrow is a storehouse of pleuripotential mesenchymal stem cells.  These stem cells, under the appropriate stimulus, have the capacity to turn into bone, cartilage, or muscle forming cells.

As essential as marrow is to life, there are several diseases, such as myeloma and leukemia, which target bone marrow.  In such cases, bone marrow transplantation, along with radiation and/or chemotherapy, can be life saving.

Your skeleton is an amazing organ, and a few of its major functions are outlined above.  In future columns we`ll talk about proper care of and common problems that affect this remarkable structure.