Birthdays and Bones

Here's a question: how many of you sneak a peek when you're in the gym locker room? Be honest. I'm one of the few who openly admits I'm a gawker (of course, I do it with utmost discretion). The locker room affords the rare opportunity to see real bodies, not those computer enhanced, airbrushed renditions we see in the media. You get a unique double feature in the locker room: bodies of all ages and bodies that are naked (unfortunately in my locker rooms, they’re also all female, but you can’t win ‘em all). For someone like me, who’s enamored of form and function, it makes for some interesting viewing.

It’s astounding how the body morphs as we age. This morning at the gym, I wrapped up my workout and was cruising to the showers when I happened by the Jacuzzi. Percolating within the bubbly froth were six elderly ladies, happily chatting away as they simmered to pruned perfection. Gazing upon that veritable senior stew got me thinking about my own aging body. Sure, the mirror is a constant reminder of the ticking, gravitational clock, and our skin holds few secrets about the passing years, but how often do we contemplate the toll age takes on our skeletons? 

Let's take a quick glimpse at the life of our bones.

We tend to think of our skeleton as fixed and unchanging, that steely scaffold on which our flesh and blood is suspended. But our skeleton is a highly dynamic structure, constantly changing throughout our lifetime.

Bone is made up of two primary components: the large protein, collagen, which gives the bones their elasticity; and hydroxyapatite, the dense inorganic substance that provides their strength (pound for pound, bone is stronger than steel!). The duality of these two main ingredients is what allows bone to be strong yet somewhat flexible and this same successful recipe is found in all mammalian skeletons.

The typical adult sports 206 bones, yet we emerge from the womb with over three hundred. Where do the others go?

They don’t go anywhere. Many of the bones that make up the newborn skeleton originate in segments that fuse over time. Many baby bones also have yet to ossify (video!), meaning they are still primarily cartilage but will eventually turn to bone (that’s what makes infants so darn flexible). And some bones, such as your kneecap, won’t show up until after you are born.

The hand is a perfect example. A newborn’s hand will eventually ossify into the twenty-seven bones that form this remarkable appendage, and that, along with the twenty-six bones of each foot, make up over half of your entire skeleton!

Bones grow in two directions: they get thicker and they get longer. Length is acquired via the growth plates at the ends of bones. These plates, or epiphyses, will continue to add bone until growth ceases and the seam that separates the plate from the shaft eventually disappears. Since each bone fuses on its own schedule, they provide a handy means of determining the age of children at the time of death.

For example, say we find a skeleton whose bones are completely fused except for the collarbone. Since your collarbone is the last to fuse – usually not until you’re in your early twenties – we can surmise the individual was a young adult when they died.

Just because the bones have stopped growing does not mean they remain unchanged. In fact, once your skeleton stops growing, it begins the slow march toward death. The little metabolic factories that produce bone (the osteoblasts) begin to slow down, and if they can’t keep pace with the bone destroyers, or osteoclasts, bone density diminishes and the skeleton becomes frail. That’s why the elderly are prone to breaks – bone loss equals bone weakness, and fractures are the typical result ("I’ve fallen and I can’t get up.").

There are many factors (aside from the number of candles on your cake) that age a skeleton. Our genetics can help or hinder; changes in hormones can wreak havoc on bone density; and then there’s lifestyle, that most fundamental (and controllable) of causal factors. What we eat, how much we exercise, and what we smoke all affect our bones; something to think about the next time you’re lying on your couch, puffing away and munching Cheetos.

So be a good skeletal steward and take care of your bones. You only get one set per lifetime, so do everything you can to make it last.

Your bones will thank you.