Kidneys pl. : of Kidney

Example:
What kind of drinks make your Kidneys work harder?

Taxonomy
kidney, Human kidneys, urine, renal cortex, blood, free encyclopedia, renal vein, humans, Search, Articles with unsourced statements, renal artery, urinary system, kidney function, interlobar veins, History of Nephrology, Language, Elsevier, abdominal cavity.

Defination from the web:
kidneys are paired organs seen in many types of animals, including vertebrates and some invertebrates. ... Located behind the abdominal cavity in the retroperitoneum, the kidneys receive blood from the paired renal arteries, and drain into the paired renal veins. ...