**3. Pathogenesis of hypertension in chronic kidney disease**

Although the kidney is also involved in essential or primary hypertension, its insufficiency causes high BLOOD PRESSURE, contributing to 2-5 % of all cases of hypertension or half the cases of all forms of secondary hypertension (Kaplan, 2006b). The pathogenesis of hypertension-related to CKD is complex and multifactorial, mainly in the late stages of the renal disease. In addition to the classical factors, such as increased intravascular volume and excessive activity of the RAS, there are new recognized players such as increased activity of the sympathetic nervous system, endothelial dysfunction and alterations of several humoral and neural factors that promote an increase of the blood pressure. Hypertension is highly prevalent in CKD, being related with the level of renal function, the etiology of the kidney disease and the age of the patient. Patients with vascular disease, diabetes and polycystic kidney disease (PKD) are more prone to be hypertensive (Ridao et al., 2001). It is also known that as renal function worsens the prevalence of hypertension increases. Therefore, more than 80 % of the patients beginning renal replacement therapy have high blood pressure (Ridao et al., 2001, USRDS, 2010).
