Which system encompasses structures involved in the secretion of hormones?

The endocrine system is the correct answer because it is specifically responsible for the secretion of hormones, which are chemical messengers that regulate various physiological processes throughout the body. Hormones are produced by glands such as the thyroid, adrenal glands, and pituitary gland, and they play vital roles in processes such as metabolism, growth, mood regulation, and maintenance of homeostasis.

In contrast, the nervous system transmits signals between different parts of the body and controls immediate responses, but it does not primarily focus on hormone secretion. The integumentary system is related to the skin and its appendages, primarily serving functions like protection and sensation, rather than hormone production. The immune system is involved in defending the body against infections and diseases and does not function in hormone secretion either. Thus, the endocrine system is the only system specifically dedicated to the production and regulation of hormones.