Which description correctly characterizes the endocrine system?

• A. Glands secrete hormones that regulate processes such as growth, reproduction, and nutrient use by body cells
• B. Transports oxygen and nutrients around the body
• C. A system of organs that exchange gases with the environment
• D. A network of tissues that defend against infection

Answer: (A)

Glands secrete hormones that regulate processes such as growth, reproduction, and the way body cells use nutrients. This hormonal signaling—chemicals traveling through the bloodstream to distant targets—defines the endocrine system and coordinates longer-term changes in the body. It’s distinct from other systems: the circulatory system mainly transports substances like oxygen and nutrients, the respiratory system exchanges gases with the environment, and the immune system defends against infection. Hormone signaling can be slower to start than nerve signals but tends to have lasting effects across multiple tissues.