What happens when things go wrong? A vicious circle.
If the blood pressure is too high for a while then the heart may stop pumping efficiently (‘heart failure’). This reduces the blood supply to the kidneys, causing them to retain salt and water and send signals to increase the blood pressure even more. This causes fluid build-up and increased pressure in the main veins, which makes the heart failure worse. Heart failure can also reduce the efficiency of kidney filtration.
Many types of kidney damage cause increased production of the blood pressure controlling hormones, leading to high blood pressure. This puts an additional strain on the heart and can, in the long run, cause heart failure. High blood pressure also increases the risk of damage to the arteries, which can cause heart attacks. And vice versa, high blood pressure can damage the blood vessels in the kidney over time, damaging the filters in the kidneys (called ‘glomeruli’) and stop them working efficiently, leading to a progressive fall in kidney function.