From the Greek khronos = time and biós = life, the term chronobiology is used to refer to the science that is responsible for the study of the rhythms and periodic physical and biochemical phenomena that occur in living beings. These biological phenomena have a determined periodicity, and may or may not have temporal correspondences with environmental cycles – such as the day and night cycle, or even the tides.
The phenomena are called biological rhythms, and have varying frequencies: those that occur with a periodicity close to 24 hours are called circadians, those that have a period less than 20 hours, are called ultradians, and those that have periods greater than 28 hours, they are called infradianos.
The beginning of the study and the first ideas related to the biological clock date from the 18th century, however, it was only in the 1950s that this study became accepted worldwide, being recognized as a scientific discipline.
To better understand this study, we will give examples of these cycles: the alternation between day and night, in which we need to adapt to the difference in light, like all other animals, this rhythm is repeated every 24 hours. The woman’s menstrual cycle, on the other hand, lasts more than 28 hours, but likewise it is a phenomenon that fits the study. In addition, to finish the examples, we also mention the heartbeat, or even breathing, which are repeated in periods of less than 20 hours.
The biological clock
In order to understand how our biological clock works, it is important to proceed with a statement. Even those people who are blind, or even animals that are in the laboratory – where there are no timeless clues – biological clocks continue to be expressed continuously, which confirms the endogenous nature of the oscillations.
But how does it work, then? In our body, there is a structure called the supraschiasmatic nucleus in the anterior hypothalamus. This is considered as our biological clock, since there are some neurons that are responsible for the circadian rhythm. The information that arrives in this structure is indicative of what is happening around the organism, in the environment, bringing parameters to determine the internal reactions.
In addition, there is the pineal gland – it produces the melatonin hormone – which receives signals from the retina when night is coming, and it sends the information back to the rest of the body. The result of this are the changes in hormonal secretion, variations in body temperature, the wake and sleep cycle are established and, in addition, other biochemical changes occur, such as the availability of glucose, cholesterol, among others. For example, we can mention the growth phase of children: always, during the night, children grow more – during sleep – because it is during this period when the greatest releases of growth hormone occur.
The biological rhythm can vary from individual to individual. For example, you may have come across people who already wake up extremely well-tempered and willing, even at an early age. These are classified as individuals of the morning chronotype. Those who sleep late and feel ready only after lunch, and have their peak efficiency in the late afternoon, are classified as individuals of the afternoon chronotype.
It is through the chronobiology and biological rhythm of each one that we can determine the best times for each individual to sleep, eat, exercise, study, among other routine activities.