Which hormone regulates blood calcium levels?

Growth hormone primarily influences growth and metabolism, particularly in bones and muscles. While it has some indirect effects on mineral metabolism, it does not directly regulate blood calcium levels. Its primary function is to stimulate tissue growth and maintain overall body composition rather than managing calcium homeostasis.

Melatonin is a hormone primarily involved in regulating sleep-wake cycles and circadian rhythms. It is produced by the pineal gland and has no known direct role in calcium regulation. Instead, its functions are more associated with the modulation of sleep patterns and seasonal biological functions, making it irrelevant to blood calcium levels.

Norepinephrine is a neurotransmitter and hormone that is part of the body's response to stress, often increasing heart rate and blood pressure. Although it can influence metabolic processes, it does not participate in the regulation of calcium levels in the blood. Its primary role lies in the sympathetic nervous system's fight-or-flight response.