What are the chemical substances called that are produced in glands and regulate various body functions?

The correct answer is hormones because these are the chemical substances produced by various glands in the body that play a crucial role in regulating numerous physiological processes. Hormones are secreted directly into the bloodstream and can influence a wide range of functions, including metabolism, growth and development, tissue function, and mood regulation.

Unlike enzymes, which are biological catalysts that facilitate chemical reactions but do not regulate bodily functions directly, hormones have a more systemic influence throughout the body. Vitamins are organic compounds that are essential in small amounts for various metabolic processes but are not produced by glands for regulatory functions. Neurotransmitters, while crucial for communication between nerve cells, operate primarily in the nervous system rather than serving as broad regulatory agents within the body like hormones do.