The body's slow chemical communication system, consisting of glands that secrete hormones into the bloodstream, is the

• A. Nervous system
• B. Endocrine system
• C. Immune system
• D. Circulatory system

Answer: (B)

Think of chemical signals that travel through the blood to reach distant targets—that describes the endocrine system. Glands such as the pituitary, thyroid, adrenal, and pancreas release hormones into the bloodstream, and these hormones bind to receptors on various cells to regulate their activity. This mode of communication is slower to start but tends to produce longer-lasting effects, coordinating processes like metabolism, growth, and stress responses across the body. The circulatory system acts as the highway that carries these hormones, but the system defined by glands and hormones is the endocrine system. In contrast, the nervous system uses fast electrical signals for quick, precise responses, and the immune system relies on immune cells and antibodies rather than circulating hormones as its primary messengers.