endocrine signaling

Endocrine signaling is communication by long-distance mail. A cell writes a message — a hormone — drops it into the bloodstream, and the circulatory system carries it across the body to recipients it will never physically touch. It is slow compared with a nerve impulse, but it can reach the whole body at once.

Technically, endocrine signaling is a mode of cell communication in which a secreted hormone enters the blood and acts on target cells located at a distance from the secreting cell. It is one of several signaling modes distinguished by how far the messenger travels: contrast it with paracrine signaling (to nearby cells), autocrine signaling (back to the same cell), and neuroendocrine signaling (from a neuron into the blood).

Because the message is diluted in the entire blood volume, endocrine signaling depends on very high receptor sensitivity and on the body limiting which cells carry receptors. A caveat: the categories overlap. A molecule can act in an endocrine fashion in one setting and a paracrine fashion in another — the labels describe the route on a given occasion, not a fixed property of the molecule.