Neil Armstrong on Being a Nerd

Bone Metabolism and the Effects of Spaceflight on the Skeleton

Bone metabolism is an ongoing mechanism that facilitates the remodeling of bones by replacing older skeletal tissue with new skeletal tissue (Clément, 2005, p. 180).  This process needs a variety of minerals such as calcium for example to generate healthy new bones, and has three different steps in the following order: 1. Reabsorption of the old tissue by the osteoclasts; 2. Reversal of the tissue when new bone cells begin to form; 3. Formation of new bone tissue by osteoblasts to replace the old tissue that has been reabsorbed (Hadjidakis and Androulakis,  2007, n.d.). The repair of fractures is when bone metabolism is noticed in action. However, bone metabolism is also crucial to continuously maintain a healthy bone architecture by repairing small damages that occur during exercising or any sort of physical effort for example. Plasma calcium homeostasis is also maintained during the process of bone metabolism (Hadjidakis and Androulakis,  2007, n.d.).

Space flight does have a strong effect on bone metabolism, and the main reason behind it is that the process of bone remodeling in Earth creatures has been going on for millions of years in the environment of the planet’s gravity. Once in space, the skeletal system is exposed to microgravity, and can be affected just like other systems in the human body. Microgravity leads to a loss of almost two percent in bone minerals (Clément, 2005, p. 188). For example, calcium loss has been noticed in humans as well as animals that spent any time between one week and one year in space, and the loss progressed the longer the time spent in microgravity. A one year mission led to a loss of about 25 percent of the total calcium in the body (“Bone Metabolism,” n.d.). Bone loss has been noticed primarily in the lower body skeletal tissue, and the bones that take most of the body’s weight, which displayed a loss in collagenous matrix. Besides this it has been noticed that both the number and size of bone cells decrease in microgravity (“Bone Metabolism,” n.d.).

The current countermeasures available to the effects of microgravity on bone metabolism include nutritional supplements and exercising. Artificially created gravity could be a solution for future longer missions, but so far this method was not found to be practical from an economic and technical point of view for shorter trips (“Bone Metabolism,” n.d.).

References:

“Bone Metabolism”. ASCI513 Presentation 5 Part 2. Retrieved from https://erau.blackboard.com/bbcswebdav/pid-14006343-dt-content-rid-2666676_4/institution/Worldwide_Online/ASCI_513/PDFs/Module_5b.pdf

Clément, G. (2005). Fundamentals of space medicine. Secaucus, NJ: Springer.

Hadjidakis D.J., Androulakis, I.I. (2007). Bone remodeling. Ann N. Y. Acad. Sci. 2006 Dec; DOI: 10.1196/annals.1365.035