Which system consists of glands that control many of the body's activities by producing hormones?

The endocrine system is the correct choice because it is specifically responsible for regulating various bodily functions through the production and release of hormones. These hormones act as chemical messengers that travel through the bloodstream to organs and tissues, influencing a wide range of physiological processes such as growth and development, metabolism, and mood regulation.

Hormones produced by the glands in the endocrine system, such as the pituitary, thyroid, adrenal glands, and others, work to maintain homeostasis in the body. For example, insulin from the pancreas helps regulate blood sugar levels, while thyroid hormones influence energy metabolism. This system operates in a slower but more prolonged manner compared to the nervous system, which transmits signals through neurons.

In contrast, the nervous system primarily communicates through electrical signals to control immediate responses and quick reflexes. The respiratory system is responsible for the exchange of gases, while the musculoskeletal system provides structure and movement to the body. Each of these systems plays crucial roles, but it is the endocrine system that is uniquely identified by its hormone-producing glands and their regulatory functions.