Hormones are best described as what type of substances?

Hormones are best described as chemical messengers that affect other tissues. They are produced by glands in the endocrine system and are released into the bloodstream, allowing them to travel throughout the body to target specific organs or cells. Once they reach their destination, hormones bind to specific receptors and initiate biological responses vital for regulating various physiological processes, including metabolism, growth, mood, and reproductive functions. This ability to influence the activities of other cells and tissues at a distance underscores their role as chemical messengers in the body.

The other options do not accurately represent the primary function of hormones. Enzymes, while also crucial for biochemical reactions, serve a different role in catalyzing reactions rather than sending signals between systems. Structural proteins provide support and shape to cells and tissues but do not have signaling functions. Ions play a critical role in electrical activity and signaling but do not specifically fit the definition of hormones as chemical messengers.