Which molecules act as chemical messengers produced by endocrine glands and travel through the bloodstream to influence behavior, emotion, and bodily functions, typically slower but longer-lasting than neurotransmitters?

• A. Hormones
• B. Neurotransmitters
• C. Enzymes
• D. Receptors

Answer: (A)

Endocrine signaling uses chemical messengers called hormones produced by glands such as the pituitary, thyroid, and adrenal glands. These hormones travel through the bloodstream to distant target cells and organs, coordinating wide-ranging changes in metabolism, growth, stress responses, mood, and other bodily functions. Because they circulate systemically and act on many areas of the body, their effects tend to develop more slowly and last longer than those of neurotransmitters, which operate quickly at specific synapses to produce fast, localized signaling. Enzymes are biological catalysts that drive chemical reactions, not messengers, and receptors are the proteins that receive signaling molecules and translate the signal into a cellular response, but they are not the traveling messengers themselves.