JET LAG
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Living organisms are accustomed to
periods of night and day alternating at set intervals. Most of the
body's regulating hormones follow this cycle, known as circadian
rhythm. In Latin, circa means almost and dies means day. These
cycles are not by themselves exactly 24 hours long, hence the
"circa." Each chemical has its own cycle of highs and lows,
interacting with and influencing the other cycles. Body temperature,
sleepiness, thyroid function, growth hormone, metabolic processes,
and the newly discovered sleep hormone melatonin all cycle with
daylight. There is a direct connection between the retina (where
light hits the back of the eye) and the part of the brain that
controls all these hormones. Artificial light has some effect, but
sunlight has much more.
When people are without clocks in a compartment that is completely
closed to sunlight, most of them fall into a circadian cycle of
about 25 hours. Normally, all the regulating chemicals follow one
another in order like threads in a weaving pattern. Every morning
the sunlight resets the cycle, stimulating the leading chemicals and
thus compensating for the difference between the 24 hour day and the
25 hour innate rhythm.
This was fine for centuries. It even accommodated those early
navigators like Magellan who sailed slowly around the world. Each
day the sun reset the clock and all the cycles fell into place.
Today, technology has surpassed adaptability, at least momentarily.
In a single day, we can completely reverse the night-day rhythm by
flying to the other side of the earth. The chemicals are thrown into
confusion like an armada without a compass or flagship. Most people
reset their rhythms within a few days, demonstrating the
adaptability of the human species. Some people, however, have upset
rhythms that last indefinitely. |
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