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.

• • 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!