Hormone

A HORMONE is a chemical secretion from a glandular part of the body which is poured DIRECTLY INTO THE BLOOD and acts on distant TARGET ORGANS or cells of the same individual, bringing about coordination between distant parts of the body.

Four elements make a complete definition, each a place where a mark can be lost: a CHEMICAL from an ENDOCRINE (ductless) gland, released DIRECTLY INTO THE BLOOD, acting on a distant TARGET ORGAN, and needed only in MINUTE quantities.

Hormones are sometimes called CHEMICAL MESSENGERS, and that phrase is worth using.

THE CONTRAST with nervous control, which examiners like: nervous coordination is FAST and SHORT-LIVED, travelling along nerves to a precise point; hormonal coordination is SLOWER but longer-lasting and more widespread, travelling in the blood to the whole body. The two together coordinate the organism.