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).
The pineal gland secretes the hormone melatonin, which is involved in the control of circadian rhythms
Circadian rhythms
circadian
True
yes
daily cycles
Yes
epinephrine
Circadian rhythms are a living organisms day/night cycles, daylight interacting with body hormone chemistry.
circadian
Our Circadian Rhythms