Cycles of Nature: Introduction

Chronobiology is the study of cycles in nature.  What kinds of cycles?  And why? 

Look at this list of a few things that have a rhythmic nature.  Chronobiology attempts to understand the cycles in nature, and what purpose they serve, in order to better understand ourselves and our world:
  • Blood pressure and heart rate both go up during the day and down at night
  • Body temperature has predictable daily highs and lows  (Fig 2.2)
    • Normal body temperature is 37.0°C (98.69F), your temperature actually swings up and down by as much as a degree or more every day as seen in this graph of a man’s temperature taken every 15 min for 5 days.
      Figure 2.2

  • Potassium excretion levels are higher at night, and lower in the day
  • Salt excretion in the urine normally follows this same pattern
  • Aldosterone levels in blood go up at night, and down during the day
  • Melatonin levels rise sharply as you begin to feel less alert, and drop when you awake
  • Hibernation is an annual cycle in some animals, such as squirrels and bears
  • The tides also exhibit cyclic patterns, even more complex than circadian!