What is the primary function of the endocrine system?

The primary function of the endocrine system is to regulate and integrate the body's metabolic activities. This system comprises glands that secrete hormones directly into the bloodstream, which then travel to various organs and tissues to exert their effects. Hormones play critical roles in numerous physiological processes, including growth, metabolism, and mood regulation, allowing the body to maintain homeostasis.

By coordinating these complex metabolic activities, the endocrine system ensures that energy production and consumption are balanced, influences how the body responds to stress, and manages reproductive functions among other vital tasks. This regulatory capability is essential for maintaining overall health and adapting to changes both internally and externally.

While the other options mention important functions such as protection, digestion, and immune response, these are primarily managed by other systems in the body. The immune response is coordinated by the immune system, digestion is predominantly facilitated by the digestive system, and physical protection falls under the musculoskeletal and integumentary systems. Overall, the integration and regulation of metabolic activities is the unique and central role of the endocrine system.