Who knew that every organ in our body operates on its own internal time clock, with the totality of the body’s organ systems synchronized by a “master pacemaker” in the anterior hypothalamus, linking our internal rhythms with events and conditions in the surrounding environment?
When this complex orchestration is working well, we don’t even notice. When it’s disrupted — in jet lag, shift work, and some illnesses — the inside and the outside don’t match up, and we’re out of sync within ourselves, as well. Literally, according to Gregor Eichele at the Max Planck Institute, “the clocks associated with individual organs in the body adapt to the new time at different speeds. As a result, the body’s physiological processes are no longer coordinated.”
Our bodies participate in an ongoing dance with the rest of the world. Some cells (sensory receptors) bring new information about what’s happening outside, and all cells communicate back and forth among and within themselves, continually. Not only neurons, but heart cells, hair cells, red blood cells — every tiny part of us is busily sending and receiving signals, organizing itself internally and integrating with everything around it. We become entrained with the larger rhythms that shape our world, whether we mean to or not.
“Circadian rhythm” is the orderly sequence through which our body temperature, metabolism, and states of consciousness fluctuate throughout each 24-hour period, in sync with the coming and going of sunlight in our immediate environment. The circadian clock coordinates all the bodily processes that maintain vitality, health, growth, and capability for reproduction.
Graphic from Xiaoyong Yang (2010), A wheel of time: the circadian clock, nuclear receptors, and physiology. Genes & Development, 24, 741-747.
You can map out your body’s predictable daily ups and downs with this online “Daily Rhythm Test” from the BBC. (Patterns of energy abundance throughout the day vary for the morning people and the evening people among us.) And you can learn more about cell signalling, the technical term for communication within and between cells, in an online tutorial available here.
BTW, we’re not the only ones. All living beings — plants, animals of the land, sea, and air, and even Neurospora crassa (bread mold!) — share a “master clock” mechanism by which they tune into the daily cycles of time. Like us, they align their rhythms with the larger processes in which they are embedded, maintaining the dynamic homeostasis that supports life.
It’s this intricate system that’s disrupted when we cross time zones: our body is still expecting the sun to rise and set when it did in the place of origin, and has to adjust to the timing that’s in effect in the place of arrival. Information about incident light enters through the eyes, and all our organs scramble to synchronize with the new schedule, and with each other. The problem is that some (such as the adrenal glands) are at the front of the line, while others lag far behind. Get with the program, guys!
There now. Even jet lag takes a back seat to contemplating the wonders of creation.