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.
Biological clocks and circadian rhythms are both mechanisms that regulate physiological processes in organisms based on time. A biological clock refers to the internal timing system that can govern various cycles, including circadian rhythms, which specifically operate on a roughly 24-hour cycle. While both serve to synchronize an organism's functions with environmental cues, biological clocks can encompass a range of time scales (e.g., ultradian or infradian rhythms), while circadian rhythms are strictly tied to the day-night cycle. Ultimately, circadian rhythms are a subset of the broader category of biological clocks.
Melatonin