Blood Pressure Basics

Blood does not travel in a steady flow through the body. Instead it is propelled through the blood vessels with the force of every heartbeat. Here's a brief overview of blood pressure.

Every organ and tissue in your body requires a constant supply of blood. This blood supply provides the oxygen and nutrients your body needs to perform its normal functions and to dispose of the waste products that result from these functions.

To meet these needs, the heart has to pump blood through about 60,000 miles of blood vessels that wind their way to and from even the most distant tissues from the heart. This blood-vessel maze is more than twice the earth's circumference. To navigate it, a certain amount of force is required to propel blood through the body and return it to the heart. Blood pressure is that force.

Your body generates blood pressure in two main ways:

1. Blood flowing through the arteries (vessels that carry blood from the heart to the tissues) creates pressure. The more blood the heart pumps with each heartbeat, the greater the amount of blood flowing through the arteries, and thus the greater the pressure against the artery walls.
2. The arteries themselves create pressure by resisting blood flow. Small arteries contain smooth muscle cells, which contract and expand like any other muscle in your body. When these muscles contract, the opening in the artery becomes smaller, and the pressure inside the artery increases as blood flows through.

The amount of pressure required to circulate blood varies according to your body's needs. For example, your body requires less blood when you're sitting still or sleeping than when you're exercising or doing strenuous work. A complex mix of hormones and nerves regulates blood flow in response to your body's changing needs.

In many people, this regulatory system goes awry and blood pressure remains persistently high, even at rest, resulting in a condition called high blood pressure, or hypertension. High blood pressure is one of the most important risk factors for stroke and heart attack.