organ kidney A paired organ of the urinary tract which has the production of urine as its primary function. AAO:0000250 BTO:0000671 CALOHA:TS-0510 EFO:0000929 EMAPA:17373 EV:0100096 FMA:7203 GAID:423 MA:0000368 MAT:0000119 MESH:D007668 MIAA:0000119 One of either of a pair of structures lying on either side of the dorsal aorta in which fluid balance is regulated and waste is excreted out in the form of urine.[AAO] OpenCyc:Mx4rvVjlYpwpEbGdrcN5Y29ycA UMLS:C0022646 XAO:0003267 galen:Kidney reniculate kidney