Which system is responsible for producing hormones that regulate metabolism?

The endocrine system is the correct choice because it is specifically designed to produce and secrete hormones that regulate a wide array of bodily functions, including metabolism. Hormones are chemical messengers that travel through the bloodstream to target organs, where they can initiate various physiological responses. In terms of metabolism, hormones such as insulin, glucagon, thyroxine, and cortisol play crucial roles in managing how the body processes and utilizes energy.

The other systems mentioned play important roles in the body but do not primarily function to produce hormones regulating metabolism. The respiratory system is mainly responsible for gas exchange, ensuring that oxygen enters the bloodstream and carbon dioxide is expelled. The digestive system focuses on breaking down food into nutrients for energy and does not primarily produce hormones for metabolic regulation. The nervous system, while it can influence metabolic processes through neurotransmitters and signals, primarily handles communication and control within the body rather than hormone production. Thus, the endocrine system is unique in its direct responsibility for hormone production and regulation of metabolism.