Kidney. Historical illustration of the anatomy of the kidney. At top, the kidney (brown) is shown with its blood vessels, the renal arteries (red) and veins (blue). At upper left of the kidney is the adrenal gland (yellow), also at centre and centre right. At bottom is a section through a kidney showing its convoluted inner surface and the ureter (yellow) that drains urine away to the bladder (not seen). The human body's two kidneys filter nitrogenous waste (mostly urea) from the blood and excrete it as urine. Also shown are the microscopic structure of the kidney (lower right) and its tubes (centre left). Colour lithograph by Fairland from The Viscera of the Human Body, 1840.