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In 90 to 95% cases the cause of hypertension is unknown, hence-the term primary hypertension.In the remaining 5 to 10%, a more discrete mechanism can be identified, and the condition is termed secondary hypertension.The kidneys play an important role in blood pressure regulation and are both a cause and victim of hypertension.Elevated blood pressure can damage the kidneys and lead to chronic kidney disease.In turn, renal disease itself can cause renovascular hypertension.Hypertension occurs earlier, is more common and tends to be more severe in patients with renal cortical disorders, such as glomerulonephritis, than in those with disorders affecting primarily the renal interstitium such as reflux or analgesic nephropathy.Activation of rennin-angiotensin-aldosterone system and retention of salt and water owing to impairment in excretory function and leading to an increase in blood volume are two main mechanisms responsible for bilateral renal hypertension.However, small proportion of renal hypertension is due to unilateral disease-mainly unilateral renal artery stenosis.Unilateral ischemia results in a reduction in the pressure in afferent glomerular arterioles.This leads to an increase in the production and release of renin from the juxtaglomerular apparatus with a consequent increase in angiotensin Ⅱ.This is usually connected with severe, difficult to control elevated blood pressure even with optimal medication.However, nowadays new percutaneous treatments for resistant hypertension are available.For example, during a catheter-based radiofrequency ablation renal sympathetic nerves are disrupted, which serves as effective anti-hypertensive treatment.