November 11, 2009
On a cosmic scale, most bodies oscillate. Stars and planets rotate (which is a kind of oscillation). Observing the spots on the sun some 400 years ago, Galileo first made the discovery that our star rotates on its axis every 25 days — an observation which even now is not fully understood. Of course the rotation of the sun does not affect us nearly as much the rotation of earth.
All life on our planet, down to its very simple forms, cyanobacteria, have adapted to the daily rotation and regular light changes. Living organisms anticipate transitions, adapt their physiology, and perform activities at advantageous times during the day.
We humans do not escape the rule. The daily rotation of the earth influences the rhythm of our existence, determines our activities, shapes our lives and has a critical influence on our physiology.
This fine tuning of our physiology and behaviour to the night-day cycle is critical. “It probably helps conserve our functions for when we need them most – a variation on the hibernation theme in animals,” commented Prof Garret FitzGerald, Professor of Medicine & Pharmacology at the University of Pennsylvania.
Speaking at the inaugural Joan Kearney Science Lecture held in the Science Department of Alexandra College in Dublin, Prof FitzGerald explained how circadian rhythms (‘around a day’ rhythms) regulate the physiological functions that occur in the body within a 24-hour period.
“All of us have a periodicity. The existence of a circadian pattern of sleep-wake cycles, fasting/feeding rhythms, fluctuations in body temperature, but also heart rate, blood pressure, platelet counts, lung function and hormone release has long been known,” he said.
“And we have also observed the periodicity of a number of related conditions such as asthma and heart attack.”
But the question that had for long remained unanswered is how all those rhythms were established and maintained. The recent development of molecular biology provided some elements of answer.
The master clock
Most cells are incapable of receiving direct input from light. They rely on a ‘master clock’ to provide time cues. In humans this circadian pacemaker is located in the hypothalamus, more specifically in a cluster of nerve cells called the suprachiasmatic nucleus (SCN).
“There are specialised cells in the retina that connect directly to the SCN and transmit the resetting signal from sunlight,” Prof FitzGerald explained. Neurons in the SCN entrained by light thus control the sleep/wake pattern, and indirectly influence the daily cycle of feeding and starvation. “The SCN is the conductor of the circadian orchestra,” Prof FitzGerald said.
Comment from Leslie
Mark my words – living with the cycles of the universe IS the Holy Grail….the fountain of youth – and the wellspring of health.