Explaining high blood pressure

Ask the doctor

Q. What causes high blood pressure?

A. My answer is going to start in your back yard; stay with me. You're holding a hose, you turn on the water, and it shoots through the hose and out the nozzle. The water is moving because it's under pressure. Similarly, when your heart beats it creates pressure that enables your blood to "water" your body with the nutrients that are in your blood.

Three things affect the amount of pressure that pushes blood through your body: how forcefully the heart pumps, how much blood there is, and how narrow the smallest blood vessels are. That last one may need some explanation. When you're watering plants, and you want the stream of water to go farther, what do you do? You make the nozzle smaller. Narrowing the opening through which the water flows increases the pressure, and the water then is able to reach the distant flowerbed.

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