Your kidneys are essential for blood pressure control. As blood passes through your kidneys, special cells "measure" blood pressure in the blood vessels leading to your kidneys (renal arteries) and adjust the amount of the hormone renin that they secrete.

Renin controls the production of two other hormones that regulate arterial pressure:

• Angiotensin, which constricts your arteries
• Aldosterone, which increases your blood volume by decreasing the elimination of water and salt through your urine

If your renal arteries become narrowed (usually due to atherosclerosis), less blood flows to the kidneys, which causes blood pressure to rise.

Renovascular disease is caused by:

• Atherosclerosis, which is the blockage or hardening of your renal arteries. It causes 8 or 9 out of 10 cases of renovascular disease. Since atherosclerosis is rarely limited to only the renal arteries, your doctor will probably suspect that you suffer from this cause of secondary hypertension if you have other forms of atherosclerosis.
• Fibromuscular dysplasia, a connective tissue disorder, which causes 1 or 2 out of 10 cases of renovascular hypertension and generally affects young women. By disrupting the connective tissue around the renal arteries, fibromuscular dysplasia causes your renal arteries to pucker into a series of tightened, beadlike pockets. This puckering is very disruptive to the cells that would ordinarily measure pressure in these arteries.