Which term refers to a chemical produced by a gland, carried by the blood which alters the activity of one or more specific target organs and is then destroyed by the liver?

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

Answer: (A)

Chemical messengers released by glands that travel in the bloodstream to regulate distant organs fit the idea of a hormone. Hormones are produced by endocrine glands, circulate through the blood, and alter the activity of specific target organs by binding to receptors. They are eventually broken down by the liver, which helps end the signal. This makes hormone the best term for the description.

Enzymes are biological catalysts that speed up reactions, not signals sent through the blood to control organs. Nerves transmit information as electrical impulses, not mainly as blood-borne chemicals. Antibodies are immune proteins that circulate to fight pathogens, not signals that regulate organ activity in the job described.