What type of glands makes up the endocrine system?

The endocrine system is specifically comprised of hormone-secreting glands, making the selection of hormone-secreting glands the correct answer. These glands produce and release hormones directly into the bloodstream, which then travel throughout the body to tissues and organs, regulating numerous physiological processes such as metabolism, growth, reproduction, and mood.

Hormonal signaling is crucial for maintaining homeostasis, and the glands within the endocrine system include the pituitary gland, thyroid gland, adrenal glands, and pancreas, among others. Each of these glands plays a unique role in producing specific hormones that trigger various responses in the body's systems, illustrating the importance of hormonal communication in biological functions.

Other types of glands mentioned, such as nerve glands and muscle glands, do not exist in the context of the endocrine system. Exocrine glands, while relevant in human physiology, differ in function; they secrete substances through ducts to the outside of the body or into the digestive system, rather than directly into the bloodstream. This distinction clarifies the specialized role of hormone-secreting glands within the endocrine system.