Hypertension is referred to as essential, or primary, when the physician is unable to identify a specific cause. It is by far the most common type of high blood pressure. While the causes of this type are unknown, they are likely to be a complex combination of genetic, environmental, and other factors.
A number of genetic factors play a major role in essential hypertension. Scientists are very interested in the genes that regulate a group of hormones known collectively as the angiotensin-renin-aldosterone system. This system plays a role in all aspects of blood pressure control, including how narrow or wide the blood vessel are, and sodium and water balance.
Experts believed that this system evolved millions of years ago to protect early humans during times of drought or stress. With industrialization, however, this system wreaks havoc on modern day people by intensifying the effects of our high-salt diets and sedentary lifestyle.
Inherited abnormalities in the nervous system
Studies suggest that some people with essential hypertension may inherit abnormalities of the sympathetic nervous system. This is the part of the nervous system that controls heart rate, blood pressure, and how narrow or wide the blood vessels are.
High blood pressure is strongly associated with diabetes, both types 1 and 2. For people with type 1 diabetes, kidney damage is generally the cause of high blood pressure.
For people with type 2 diabetes, being overweight or obese is associated with high blood pressure. Oddly, however, even thin people with type 2 diabetes often have high blood pressure. Scientists believe that the inability of the body to use insulin (called insulin resistance, the cause of type 2 diabetes) may lead to retention of sodium -- a contributor to high blood pressure.
In any case, people who have diabetes plus high blood pressure have a greater chance of heart attack, kidney disease, and stroke than people who have high blood pressure alone.
Obesity, on its own, has a number of possible effects that could lead to high blood pressure. For example, being overweight means the heart has to pump more blood to supply the extra tissue in your body. The larger blood volume increases the work of the heart and the pressure on blood vessels. Weight loss is a good way to return blood pressure to normal.
Low levels of nitric oxide
Nitric oxide (a gas) is produced in the body and helps keep muscle cells that line blood vessels relaxed and flexible. It may also help prevent blood from clotting. Low levels of nitric oxide have been measured in some people with high blood pressure (particularly in African Americans) and may be an important factor in essential hypertension.
Review Date: June 3, 2003
Reviewed By: Jacqueline A. Hart, M.D., Department of Internal Medicine,
Newton-Wellesley Hospital, Harvard University and Senior Medical Editor,
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