Which term describes a chemical released by an endocrine gland that travels in the blood to influence distant organs?

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

Answer: (A)

A hormone is a chemical messenger released by an endocrine gland into the bloodstream. It travels through the blood to distant organs that have specific receptors for it, and when it binds to those receptors, it triggers a response in the target tissue. This system lets the body coordinate activities like metabolism, growth, and reproduction across different organs. For example, insulin is a hormone released by the pancreas that helps lower blood sugar by acting on liver and muscle cells.

Enzymes, by contrast, usually catalyse reactions at or near their site of release and don’t travel through the blood to distant targets. Nerves transmit signals as electrical impulses along neurons, not as circulating chemicals in blood. Antibodies are immune proteins produced in response to pathogens, not hormones that regulate distant organs.