Mostly the suprachiasmatic nucleus (SCN) in the brain. The pineal gland is also involved.
Suprachiasmatic nucleus
circadian rhythms.
Not exactly. Circadian rhythms are a subset of diurnal rhythms. Diurnal rhythms reoccur daily and can be circadian and non-circadian. Circadian rhythms can be set by the environment (entrainment), but are not dependent on environment stimulus for continuation (free-running) (ie. hormone secretion). Non-circadian rhythms are responsive to the environment, but still operate on a daily cycle (ie. the process of photosynthesis).
Circadian rhythms
circadian
True. Diurnal rhythms refer to biological processes that follow a 24-hour cycle, while circadian rhythms specifically refer to the body's internal clock that regulates these processes over a 24-hour period. Therefore, diurnal rhythms are a component of circadian rhythms.
daily cycles
epinephrine
yes
Circadian rhythms are a living organisms day/night cycles, daylight interacting with body hormone chemistry.
Melatonin
Circadian rhythms are regulated by the suprachiasmatic nucleus (SCN) in the brain, located in the hypothalamus. The SCN receives input from light-sensitive cells in the retina, helping to synchronize internal body clocks with the external environment.