What is the primary function of the endocrine system?

The primary function of the endocrine system is to produce and secrete hormones that regulate various bodily functions. Hormones are chemical messengers that travel through the bloodstream to target organs and tissues, influencing a wide range of processes such as growth and development, metabolism, reproduction, and mood regulation. This system plays a crucial role in maintaining homeostasis—keeping the body's internal environment stable despite external changes.

The other options relate to bodily functions managed by different systems. For example, while circulation is managed by the cardiovascular system, the digestive process involves the digestive system, and immune protection is the domain of the immune system. Each of these systems contributes to overall health and function, but it is the endocrine system that specifically focuses on hormonal regulation, making it essential for coordinating and integrating physiological activities across various organ systems.