Jupiterimages/Brand X Pictures/Getty Images. Panic is a natural reaction when you're served with a subpoena, but as far as legal documents are concerned, a subpoena duces tecum is one of the more innocuous ones you can encounter.
Circadian rhythms are biological oscillations that recur with a period of approximately one day. Health issues related to circadian rhythms include jet lag, shift work, seasonal depression, and time-of-day variations in response to medical treatments.
The body clock, or circadian clock, is an internal clock that keeps track of time. Circadian comes from circa-diem meaning around a day. So in a mouse for example it is about 23.5 hours and for a human its about 24.5 hours. If you are kept in constant darkness your body will still work to around a 24-hour cycle. It is not just being driven by light and dark. It is an intracellular clock so if you look in individual cells they are all able to keep time as well. If you put cells in a dish they will show 24-hour changes in gene expression.