Kidney- singular, kidneys- plural.
The word "kidney" is singular.The plural form is "kidneys."
The organ was called a kidney first. The kidney bean is called so because it is shaped like a kidney, the organ.
An accessory kidney is an "extra" kidney.
Kidney stones. Kidney failure.
The individual units of the kidney, called nephrons, produce urine and empty into structures called collecting ducts. Many nephrons empty into a single collecting duct. Similarly, many collecting ducts empty into a minor calyx. Minor calyces empty into a major calyx, and the major calyces empty into the singular renal pelvis (each kidney has a single pelvis). The renal pelvis empties into the ureter.
Kidney disease can lead to kidney failure.
Kidney failure and kidney rejection can still remain after kidney transplant.
kidneys is the plural of kidney.
Edema means swelling. An edematous kidney is a swollen kidney.
An opisthonephric kidney is the functional kidney of anamniotes, fish, and amphibians.
Quantum is singular, not singular possessive. The singular possessive form is quantum's.