Hypertensive kidney. Light micrograph of a section through a kidney damaged by benign hypertensive nephrosclerosis. The kidney has been damaged as a result of high blood pressure (hypertension). Two glomeruli (large, round, centre left and right), damaged as a result of chronic ischaemia (restricted blood flow), can be seen. The kidneys filter waste products from the blood. Sustained high blood pressure damages the individual filtering units (nephrons), which become replaced with fibrous scar tissue, making them unable to function. As more nephrons are damaged, toxic substances start to build up in the blood, eventually leading to kidney failure, which can be fatal.