What is the endocrine system?

• A. The nervous system
• B. The body's 'slow' chemical communication system; a set of glands that secrete hormones into the bloodstream
• C. The immune system
• D. The digestive system

Answer: (B)

The endocrine system is the body's slow chemical communication system, composed of glands that secrete hormones into the bloodstream to signal distant targets. Hormones act as chemical messengers that regulate processes such as metabolism, growth, development, reproduction, and responses to stress. Because they travel through the blood, their effects start more gradually than nerve impulses, but they tend to last longer. Key players include the pituitary (often called the master gland), thyroid, adrenal glands, pancreas, and gonads, all working in feedback loops to maintain balance. In contrast, the nervous system uses fast electrical signals for quick, short-lived actions; the immune system defends the body against pathogens; and the digestive system processes and absorbs nutrients.