ABSTRACT
With the shared definition and the many overlaps among the chemicals and living systems of interest between pharmacology and toxicology, this chapter attempts to define the basic principles that drive and guide these shared interactions between chemicals and living systems. The sites to which chemicals attach to mediate the interactions that lead to effects on living systems are referred to as receptors, indicating that these are the biomolecules that receive the chemical information from the molecules with which they attach. The same kinds of chemical interaction forces lead to selective and concentration-dependent binding attachments for diverse other physiologic molecules also. Having described the importance of attachment for chemical interactions with living systems and the most important general terminology for those attachments, the authors now address the quantitative nature of chemical attachment, using the term "ligand" for the chemical entity and the term "receptor" for its target attachment site.
