Chronobiology Introduction

Chronobiology is the study of biological rhythms. Circadian rhythms, characteristics of living systems that cycle with a relatively fixed and predictable period of about 24 hours, fall into this category of study. An organism's circadian clock is usually synchronized to the 24-hour Earth day, including the day's light-dark signals and temperature changes. Space flight experiments have shown that circadian rhythms persist in the absence of environmental time cues in space, indicating that clocks regulating circadian rhythms reside within the organisms. However, some rhythms can show abnormalities relative to the light-dark cycle in space. Of special concern to astronauts is how circadian patterns of various hormones and/or metabolic processes may be altered in reduced gravity.

Body temperature regulation, like sleep and activity patterns, shows a circadian rhythm. In humans, with the exception of fever episodes, the body temperature rarely varies more that 2° C from the baseline at any time. This normal functioning of the thermoregulatory system is essential for life. Some alterations in core temperatures have been observed during space flight and suggest that the thermoregulatory system is also modified by microgravity exposure.

Teaching Goals: