Circadian Biology 🕰️

Circadian Biology

Circadian Rhythm is an approximately 24 hour internal clock; every living thing on Earth has one, from plants that open their leaves at sunrise to humans who get sleepy at night.

Our brain keeps time via a special area called the Superchiasmatic Nucleus (SCN) in the hypothalamus that acts mainly as our main clock.

Additionally, essentially every gene in the body also has its own internal clock as well, the peripheral clocks, which in normal healthy conditions should be synced up perfectly to the “central clock”

Why do we have a circadian clock?

The human body, like any dynamic thermodynamic system, operates as an energy system. The defining principle for such a system is efficiency: the ability to transduce energy from the environment with minimal loss. Energy is never created or destroyed, it is transformed. The more effectively our bodies can convert available environmental energy (from light, food…) into usable biological energy, the more efficient and resilient we are.

To achieve this efficiency, the body must accurately anticipate thermodynamic conditions and energy availability in the environment. These variables change throughout the day and across seasons, including fluctuations in light intensity, spectral composition, temperature, and food availability.

Circadian timekeeping enables humans to adapt to these changes, optimize energy expenditure, and regulate internal physiological processes in harmony with the environment. Without such a system, Homo sapiens would be unable to achieve maximal metabolic efficiency or maintain coordinated bodily functions.