High BP causes artery damage, and the kidneys are packed with arteries.
Kidneys are supplied with dense blood vessels, and high volumes of blood flow through them. Over time, uncontrolled high blood pressure can cause arteries around the kidneys to narrow, weaken or harden......this is the same for coronary arteries (heart disease) and the cerebral arteries (stroke) or indeed the legs (gangrene). These damaged arteries are not able to deliver enough blood to the kidney tissue and it slowly dies.
Damaged kidney arteries do not filter blood well.
Kidneys have small, finger-like nephrons that filter your blood. Each nephron receives its blood supply through tiny hair-like capillaries, which are the smallest of all blood vessels. When the arteries become damaged, the nephrons do not receive the essential oxygen and nutrients. Also, the kidneys lose their ability to filter blood and regulate the fluid, hormones, acids and salts in the body.
Damaged kidneys fail to regulate blood pressure.
Healthy kidneys produce a hormone to help the body regulate its own blood pressure. Kidney damage and uncontrolled high blood pressure each contribute to a negative spiral. As more arteries become blocked and stop functioning, the kidneys eventually fail. This process can happen over several years, but it can be prevented