Chemicals produced by the glands of the endocrine system that are carried by the bloodstream to other body tissues.

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Hormones are signaling chemicals produced by endocrine glands and carried through the bloodstream to distant target tissues. This allows the body to coordinate processes like metabolism, growth, and stress responses across organs that aren’t right next to each other. Endocrine glands such as the pituitary, thyroid, and adrenal glands release these messengers into the blood, and they only exert their effects where there are specific receptors on target cells. For example, insulin from the pancreas travels in the blood to tissues that regulate blood glucose.

Endorphins, while important signaling molecules, are primarily known as neuropeptides that act within the nervous system as neurotransmitters or neuromodulators, not the classic circulating messengers produced by glands to reach distant tissues. The endocrine system refers to the whole network of glands that produce these messengers, not the chemicals themselves. Resting potential is the electrical charge difference across a neuron's membrane when it’s not firing, not a chemical messenger.