ABSTRACT
Endocrinology, the study of the hormonal controls of bodily function, is one of the newer disciplines within physiology. Chemically mediated controls of physiologic function are extremely diverse. Specific chemicals mediate critical processes in nervous function such as synaptic transmission, which involves the triggered release of neurotransmitters responsible for initiating action potentials in the postsynaptic neuron. The testing of unknowns for hormone activity initially depended totally on biologic assays, or bioassays, in which the biologic response observed in test animals served as the end point. The largest group of hormonally active molecules includes several chemical forms of a size. They include biogenic amines; peptides, or small polymers of amino acids; thyronines, the iodine-containing hormones of the thyroid; steroids; and prostanoids, derivatives of long chain polyunsaturated fatty acids, especially arachidonic acid. The receptor may be viewed as a chemical transducer that must be present in a tissue if that tissue is to be a target for the hormone of interest.
