The<unk> s are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blood exits into the paired renal veins. Each<unk>  is attached to a ureter, a tube that carries excreted urine to the bladder. The<unk>  participates in the control of the volume of various body fluids, fluid osmolality, acid–base balance, various electrolyte concentrations, and removal of toxins. Filtration occurs in the glomerulus: one-fifth of the blood volume that enters the<unk> s is filtered. Examples of substances reabsorbed are solute-free water, sodium, bicarbonate, glucose, and amino acids. Examples of substances secreted are hydrogen, ammonium, potassium and uric acid. The nephron is the structural and functional unit of the<unk> . Each adult human<unk>  contains around 1 million nephrons, while a mouse<unk>  contains only about 12,500 nephrons. The<unk> s also carry out functions independent of the nephrons. For example, they convert a precursor of vitamin D to its active form, calcitriol; and synthesize the hormones erythropoietin and renin. Chronic<unk>  disease (CKD) has been recognized as a leading public health problem worldwide. The global estimated prevalence of CKD is 13.4%, and patients with<unk>  failure needing renal replacement therapy are estimated between 5 and 7 million. Procedures used in the management of<unk>  disease include chemical and microscopic examination of the urine (urinalysis), measurement of<unk>  function by calculating the estimated glomerular filtration rate (eGFR) using the serum creatinine; and<unk>  biopsy and CT scan to evaluate for abnormal anatomy. Dialysis and<unk>  transplantation are used to treat<unk>  failure; one (or both sequentially) of these are almost always used when renal function drops below 15%. Nephrectomy is frequently used to cure renal cell carcinoma. Renal physiology is the study of<unk>  function. Nephrology is the medical specialty which addresses diseases of<unk>  function: these include CKD, nephritic and nephrotic syndromes, acute<unk>  injury, and pyelonephritis. Urology addresses diseases of<unk>  (and urinary tract) anatomy: these include cancer, renal cysts,<unk>  stones and ureteral stones, and urinary tract obstruction. The word “renal” is an adjective meaning “relating to the<unk> s”, and its roots are French or late Latin. Whereas according to some opinions, "renal" should be replaced with<unk> " in scientific writings such as<unk>  artery", other experts have advocated preserving the use of renal as appropriate including in "renal artery".
Kidney
Liver
Lung
Heart
Peripheral nervous system
Central nervous system
Brain
Adrenal gland