Saturday, June 30, 2012

Homeostasis: life on the wire

A couple of weeks ago, I watched the live broadcast of Nik Wallenda's walk across a high wire suspended above Niagara Falls.  I've been a fan of the famous Wallenda family ever since I saw Karl Wallenda cross a high wire suspended above the baseball stadium in St. Louis. In my A&P classes, we often use the image of a Wallenda on a high wire as a model to help us understand a central concept of physiology . . . homeostasis.

This "Wallenda model" of homeostasis teaches us that to stay alive and well, our body must remain in "balance."  That is, our internal environment is at risk every moment . . . risk of losing the delicate balance of "just right" conditions inside our body that keep us functioning.  If we lose that balance, as Karl Wallenda (Nick's great grandfather) did in the late 1978, then we die.

Like a Wallenda's position on the wire, any physiological variable (any condition in our body that may change) has an ideal range called the set point. The oxygen content of our blood has an ideal range that keeps us healthy, just as the position of a wire walker's center of gravity must remain within a narrow range to stay on the wire (and thus alive).

When a wire walker is affected by wind, rain, distraction--as was Nik during his recent wire walk--this pushes the variable (body position) away from the set point.  If the wire walker reverses the shift by moving left when the body starts to fall to the right, then the set point position is recovered and all is well.  Likewise, when exercise causes a fall in blood oxygen content, the set point can be recovered by an increase in breathing rate . . . thus reversing the fall in blood oxygen content.

Such recovery by sensing a shift away from set point, then responding to the shift by reversing the direction of a disturbance, is called negative feedback.  This is a basic principle of how the body's organs function to keep us alive . . . they continually work to reverse disturbances to the balance of the body.

If you want to learn more about how to use my Wallenda model of homeostasis to understand the balance of the body, check out these resources:

Survival Guide Anatomy & Physiology: Tip, Techniques, and Shortcuts
Kevin Patton
Elsevier Publishing
[Includes a complete rundown of the Wallenda Model of Homeostasis]

Mini Lesson: Homeostasis
Kevin Patton
Lion Den
[Outline summarizing homeostasis.  Includes three different models to help in understanding the balance of the body, including the Wallenda Model.]

Wallenda Model
Kevin Patton
Lion Den Slide Collection
[Animated PowerPoint-compatible slide summarizing some points of the Wallenda Model.]
"Life is always on the wire.  The rest is just waiting."
Karl Wallenda
Photo (c) dpape