Kidney in renal hypertension. Cutaway illustration of the effects of high blood pressure (hypertension) on the kidneys. The blood vessels may rupture, bleeding and producing haemorrhagic lesions (red patches) within or on the surface of the kidney. The kidneys filter waste products from the blood. Sustained high blood pressure damages the kidney's filtering units (nephrons), which become replaced with fibrous scar tissue, making them unable to function. Toxic substances build up in the blood, leading to kidney failure, which can be fatal. The structure on top of the kidney is the adrenal gland (yellow). The renal vein (blue), renal artery (red) and ureter are also shown.