This is the second of our two part series on what causes high blood pressure. In this part we're going to discuss what causes secondary high blood pressure in detail.

Secondary high blood pressure is the less common form of high blood pressure with only 5% of reported cases suffering from this type which is caused by a disorder of specific organ of the body such as the kidney, adrenal gland or aortic artery.

Diseases of the kidney can be a cause of secondary high blood pressure. This is called renal hypertension because it is caused by problems with the kidneys. One of the more important and common causes of renal hypertension is the narrowing of the artery that supplies blood to the kidneys. In younger people the narrowing is caused mostly by a thickening of the wall of the arteries leading to the kidneys. In older people mostly, it is caused by a build up fat plaques that block the renal artery.

The reason that the narrowing of the artery causes hypertension is because, first, the narrowing restricts the flow of blood to the kidneys. The reduced blood supply then causes the kidney to produce the hormones, renin and angiotensin. These hormones, along with aldosterone from the adrenal gland, cause a constriction and increased stiffness in the peripheral arteries throughout the whole body, which finally results in high blood pressure.

A doctor will usual suspect renal hypertension when high blood pressure is discovered in a young person or if a new onset of high blood pressure is detected in an older person.

Another cause of secondary high blood pressure is adrenal gland tumors. There are two types of tumors and both are very rare but do occur. Both of these tumors cause the adrenal glands to produce excessive hormones which is the cause of the high blood pressure.

Another cause of secondary high blood pressure, which is usually inherited, is Coarctation of the aorta. This is a common cause of hypertension among young children. The condition is causes by a narrowing segment of the aorta, which is the main large artery that comes out of the heart. The aorta is responsible for delivering blood to all the organs of the body. The narrowing segment is usually above the renal arteries. This narrowing reduces blood flow to the kidneys.

Other genetic factors make up what is called the "metabolic syndrome". People that have metabolic syndrome have insulin resistance and a tendency to have type 2 diabetes. This is another contributing factor to secondary high blood pressure.

Then there is the problem with obesity. People who are obese have elevated levels of blood fat, vascular inflammation, endothelial dysfunction and ultimately high blood pressure. The epidemic of obesity, especially in the United States, is one of the main causes of high blood pressure today.

Now that we basically know the main causes of high blood pressure, in future articles we're going to discuss how to treat this disease and keep it under control.