Hi! I am a human and I am going to give you an overview of how circadian rhythms regulate my entire body, starting with the master clock in the brain called the SCN.

Throughout the day and in preparation for activities, the SCN tells the hypothalamus to release chemical signals that regulate the function of all the organs, through the peripheral clocks.
The thyroid gland produces high levels of  thyroid hormones T3 and T4 which help to increase metabolic rate and prepare the body for activity 
In the morning, the hypothalamus tells the clock in the heart to increase blood pressure, and heart rate, to prepare for the demands of daily activities. 
The cells of the adrenal glands secrete cortisol which is a stress hormone that helps the body cope in stressful situations. Cortisol is released at high levels during the day in anticipation of stress and decreses at night during rest.
The Pancreatic clock cells allow the body to be more sensitive to glucose during the day when the an individual is active and feeding. When this is disrupted, diabetes and obesity can occur as a result.
Growth hormone is secreted at high levels throughout the body at night when the body is resting and unlikely to encounter high levels of stress. It isn't a coincidence that high levels of cortisol also block growth hormone secretion. It would be wasteful for the body to turn on growth mechanisms when it is constantly under attack.
DNA repair mechanisms become extremely active during the day to fix any problems encountred due to sun exposure. Repair mechanisms are suppressed at night when the body is resting and will likely not encounter any damage or stress.