Which system is responsible for releasing hormones that regulate body activities?

The endocrine system is the correct answer because it is specifically responsible for producing and releasing hormones directly into the bloodstream. These hormones are chemical messengers that travel throughout the body to target organs and tissues, thereby regulating a wide variety of physiological processes, including metabolism, growth and development, tissue function, and mood.

Unlike the other systems mentioned, the endocrine system works in a more gradual manner compared to the nervous system, which provides rapid communication via electrical signals. The reproductive system is focused primarily on the functions related to reproduction and sexual health, while the skeletal system provides structure and support to the body but does not have a direct role in hormone regulation. The interplay between the endocrine system and other systems in the body helps maintain homeostasis and overall health, making it fundamentally crucial for regulating bodily functions through hormonal balance.