In order that the differentiated tissues and organs of the multicellular body should produce an integrated response to the needs of the organism as a whole their activities must be controlled, or regulated. Regulation is by chemical means. In animals there are two distinct means of deliving these chemical regulators. In the first, the nervous system, the chemical promotors or inhibitors are released directly into the target organs or tissues providing a rapid, though short-lived, mode of regulation. The release of chemical activators from nerve endings, termed neurosecretion, occurs both in the target organs and in the junctions between nerve cells, the synapses.
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