Pregnancy Induced Hypertension Article

What causes high blood pressure

The cause is not known in most cases
This is called 'essential hypertension'. The pressure in the blood vessels depends on how hard the heart pumps, and how much resistance there is in the arteries. It is thought that slight narrowing of the arteries increases the resistance to blood flow, which increases the blood pressure. The cause of the slight narrowing of the arteries is not clear. Various factors probably contribute.

(It is a bit like water in a hosepipe. The water pressure is increased if you open the tap more, but also if you make the hosepipe narrower by partially blocking the outflow with your thumb.)

Rarely, high blood pressure is caused by other conditions
It is then called 'secondary hypertension'. For example, certain kidney or hormone problems can cause high blood pressure.