Achemical substance required by the body is called

This question is rather vague however, there are numerous chemical substances that the body needs one could be neurotransmitters that are used by neurons to transmit information to other nearby neurons.

The neuron, a cell that composes the nervous system. For example a brain, an organ composed of thousands of neural fibers and glial cells that performs many important organismic functions. 

Other substance:
Hormones