critical organ

in toxicology
https://doi.org/10.1351/goldbook.15610
Organ that first attains the critical concentration of a substance and exhibits the critical effect under specified circumstances of exposure and for a given population.
Source:
PAC, 2007, 79, 1153. (Glossary of terms used in toxicology, 2nd edition (IUPAC Recommendations 2007)) on page 1199 [Terms] [Paper]