Hi I am a doberman and I will talk about the circadian system and the effects it has on my health.

Like my mammalian counterparts, the sun controls the function of the central clock in my brain which causes the hypothalamus to send control signals to the rest of my body

The hypothalamus prepares my body for a stressful day by stimulating the adrenal glands on my kidneys to produce cortisol, a stress hormone. This also increases by blood sugar levels to help me deal with activity
Next, the thyroid gland is stimulated by the hypothalamus to increase the production of thyroid hormones. This increases my metabolic rate and prepares me for feeding
First thing in the morning, the hypothalamus sends a signal to the heart to increase blood pressure, heart rate, and cardiac output. This wakes me up and prepares me for the rest of my day 
Because my body is preparing for a lot of stress, it would be wasteful to also spend energy on growth, so growth hormone levels decrease during the day and increase at night when I am resting