EXAMINING EFFECTS OF SPACE FLIGHT ON THE SKELETAL SYSTEM

CASE STUDY 5
BONE, CALCIUM, AND SPACE FLIGHT

Principal Investigator
Emily Morey-Holton, Ph.D.
NASA Ames Research Center
Moffett Field, California

INTRODUCTION

Why do we physically stop growing when we have reached less than a third of our life expectancy? Aquatic species such as mollusks, crustaceans, and some fish grow indefinitely. Can you imagine? Some of these species never stop growing! One giant clam weighed 600 pounds and may have been 100 years old; a giant squid can grow to 50 feet; a 2800 pound turtle has been reported. One reason that this is possible may be that the water in which these creatures live helps support their great weight. But landwellers, such as ourselves, have to support their body weight without this buoyant help (buoy = float), so we have evolved ways of limiting our size. Thank goodness, or otherwise, we might call our world the "land of the giants !" It is interesting, however, that studies have shown that astronauts actually become taller in space since their spinal column is not constantly being compacted by the downward force of gravity. We'll discuss this later in the chapter.

Certainly, it is not just the skeletal system that is challenged on a daily basis by the gravitational forces we encounter here on Earth. We've already discussed how gravity influences the muscles in our body. And we will discuss in this chapter some of t he connective tissues that contribute to the structure of our bodies. So, we must keep in mind that it is the components of the musculoskeletal system - bone, muscles, and connective tissue - that perform together with pe rfect teamwork. Their mission is threefold:

  • to support the body,
  • to shield our delicate internal organs, and
  • to make the body mobile.
No team has ever been more carefully equipped and organized. In this chapter, we will discuss three primary aspects of the skeletal system: the skeleton's structure and function; the formation and breakdown of bone; and the important chem icals (minerals, salts, and hormones) that participate in bone metabolism. In addition, we will examine a particular space flight investigation that was carried out to look at how bone formation and calcium metabolism change in microgravity. Let's begin w ith a look at how the Earth's gravity has influenced the development of our skeletal structure.