Which term is used for a chemical that travels in the bloodstream to affect distant target organs?

• A. Hormone
• B. Enzyme
• C. Antibody
• D. Nerve

Answer: (A)

Hormones are the chemicals that travel in the bloodstream to affect distant target organs. They’re released by endocrine glands into the blood, which transports them to specific cells that have the right receptors. This allows signals to reach far-away parts of the body, producing slower but longer-lasting effects compared to electrical nerve impulses.

Enzymes are catalysts for biochemical reactions and usually act locally, not as circulating messengers to distant organs. Antibodies are immune system proteins that patrol the bloodstream to identify and neutralize pathogens, not signaling molecules that regulate distant organs. Nerves transmit rapid electrical signals along neurons, delivering quick, short-term responses to specific areas rather than circulating chemical messengers.