Which system releases hormones that regulate metabolism and energy levels?

• A. Endocrine System
• B. Nervous System
• C. Immune System
• D. Respiratory System

Answer: (A)

Hormones are chemical messengers released into the bloodstream to control how the body uses energy. The endocrine system hosts glands that secrete these hormones, and they regulate metabolic rate, glucose use, and energy mobilization. For example, thyroid hormones set the pace of metabolism, while insulin and glucagon manage blood glucose, and adrenal hormones adjust energy availability during stress. Because these signals travel through the blood to distant targets, the endocrine system is the main regulator of metabolism and energy levels. The nervous system uses fast-acting electrical signals and neurotransmitters for quick control, not long-distance hormonal signaling, and the immune and respiratory systems aren’t the primary sources of hormones that govern metabolism.