The renal system in an anatomical system that maintains fluid balance and contributes to electrolyte balance, acid/base balance, and disposal of nitrogenous waste products..

In various sources such as Encyclopedia Britannica, the excretory and urinary systems are indeed the same system (see wikipedia talk page); we merge two BTO classes here

An anatomical system which consists of organs and tissues which produce, store, and excrete urine.[AAO]

excretory system, systema urinaria, systema urinarium, urinary tract, renal system, urinary system

uberon

renal/urinary system, renal or urinary system

Evolution of vertebrate renal anatomy appears quite conservative when compared, for example, to evolution of respiratory and cardiovascular systems in vertebrates. Major anatomical changes in vertebrates kidneys separate those of birds and mammals from kidneys of lower vertebrates. General increase in animal size from fish to mammals is reflected by an increase in total number of nephrons per kidney, rather than by constant change in tubular dimensions.[well established][VHOG]

UBERON:0001008

http://purl.obolibrary.org/obo/uberon.owl, http://purl.obolibrary.org/obo/cl.owl

http://purl.obolibrary.org/obo/NCBITaxon_110815, http://purl.obolibrary.org/obo/NCBITaxon_147099

In humans, the renal system comprises a pair of kidneys, a pair of ureters, urinary bladder, urethra, sphincter muscle and associated blood vessels, This definition is inclusive of the organs of the vertebrate renal system, as well as the Malpighian tubules of insects, and allows for future incorporation of structures such as the antennal glands of crustaceans

• kidney

• genitourinary system

• upper urinary tract

• renal filtration cell
• nephric ridge
• lower urinary tract
• upper urinary tract
• excretory tube
• embryonic cloaca