What are chemical messengers produced in one tissue and affect another?

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

Answer: (C)

Endocrine signaling uses hormones as chemical messengers produced by glands to travel through the bloodstream and affect distant target tissues. This systemic travel lets the body coordinate processes that are spread out over different organs, like how insulin from the pancreas regulates glucose uptake in liver and muscle, or how adrenaline readies the body for quick action.

Neurotransmitters are also chemical messengers, but they are released by neurons and typically act across synapses on nearby cells, not carried long distances through the blood. Enzymes are not messengers at all—they are catalysts that speed up chemical reactions. Receptors are proteins that receive signals; they respond to messengers but are not the messengers themselves.