Hypertension - Description

The circulatory system is the network of organs and blood vessels through which blood travels in the body. Blood is pumped out of the heart into blood vessels known as arteries. After passing through the body, blood returns to the heart by way of blood vessels known as veins.

As blood flows through arteries and veins, it pushes on their walls. Blood pressure is defined as the force exerted by blood inside arteries.

Blood does not flow steadily through the circulatory system. At one moment, the heart muscle squeezes blood out of the heart into the arteries. At this point, the blood pressure is high because of the force exerted by the heart. At the next moment, the heart muscle relaxes to let fresh blood into the heart. At this point, the blood pressure is lower because of reduced force by the heart muscle.

The two stages of high and low blood pressure have special names. The highest pressure reached by blood in the arteries is called the systolic pressure. The lowest pressure reached by blood in the arteries is known as the diastolic pressure.

When a doctor or nurse takes a person's blood pressure, he or she records two readings: the systolic (highest) and the diastolic (lowest) pressure. For example, a patient's blood pressure might be recorded as 140/80, which is read as "140 over 80." That reading means that the patient's highest blood pressure is 140 and the lowest blood pressure is 80.

The numbers 140 and 80 are measured in units called "millimeters of mercury" or "mm Hg." This unit is commonly used by scientists to measure pressure.

The American Heart Association considers blood pressure less than 140 and greater than 90 to be normal for adults. A person whose diastolic pressure is less than 90 is said to have low blood pressure. Someone with a systolic pressure of more than 140 is said to have high blood pressure—or hypertension.

Hypertension is a serious problem because people with the condition have a higher risk for heart disease and other medical problems than people with normal blood pressure. If left untreated, hypertension can lead to a number of medical conditions, including:

• Arteriosclerosis
• Heart attack (see heart attack entry)
• Stroke (see stroke entry)
• Enlarged heart
• Kidney damage

Arteriosclerosis is also called hardening of the arteries. The arteries are normally flexible. They expand and contract to adjust to the flow of blood through them. High blood pressure can cause artery walls to become thick and tough. The arteries themselves may become narrower. Blood cannot flow as easily through them.

When that happens, certain substances in the blood can begin to build up inside the arteries. These substances make the openings even narrower. Eventually, an artery may close completely. When that happens, blood can no longer flow through the circulatory system. A blocked artery can result in a heart attack or a stroke.

Hypertension can also damage the heart itself because the heart has to work harder to push blood through the circulatory system. It grows larger to keep up with this job. If the heart becomes too large, it may no longer be able to pump enough blood through the body. The heart may fail.

Kidneys can also be damaged by hypertension. The kidneys filter waste products from the blood. If blood vessels to the kidneys become clogged, fewer wastes are removed from the blood. The kidneys may fail and wastes may build up in the blood. About 25 percent of the people who are treated for failed kidneys have hypertension.