A chemical messenger produced by an endocrine gland and carried by the bloodstream to another part of the body is a

• A. Hormone
• B. Neuron
• C. Neurotransmitter
• D. Reflex action

Answer: (A)

A hormone is a chemical messenger produced by an endocrine gland and carried by the bloodstream to a distant part of the body. This means it can influence cells far from where it was released, by binding to specific receptors and triggering a response that is often slower to start but longer lasting. This differs from a neuron, which transmits electrical signals along nerves; a neurotransmitter is a chemical used at synapses to pass signals between neurons or between a neuron and its target cell and doesn’t travel through the blood; and a reflex action is a fast, automatic neural response, not a circulating messenger.