Which body system uses chemical messengers to regulate metabolism, growth, and reproduction?

• A. Nervous
• B. Digestive
• C. Respiratory
• D. Endocrine

Answer: (D)

The system that uses chemical messengers traveling through the bloodstream to coordinate processes like metabolism, growth, and reproduction is the endocrine system. Hormones released by endocrine glands travel to distant targets and influence how fast the body uses energy, how tissues grow, and how reproductive development occurs. For example, thyroid hormones set metabolic pace, growth hormone drives development, and sex hormones regulate reproductive function. In contrast, the nervous system relies on rapid electrical signals and neurotransmitters for quick, local responses, not the broad, long-range regulation described here.