It does so because as pressure or tension on the walls of the organs involved, for a long enough period of time, that organ accumulateds enough pressure duration, hours, to cause damage. The selective organs that seem to be affected the most would be the brain, kidneys, heart. However, in my estimation, the arterial system itself is most often involved. To say that another way, sometimes you see heart damage but no kidney damage, and sometimes you will see kidney damage but no heart. But I do not believe it targets the arterial system itself, because if the blood pressure is high enough for long enough, there are always abnormalities in the arterial system.
Abnormalities develop in the arterial system.
I feel that I should be concerned to a point. That is, the top number is higher than 140, meeting the definition for systolic hypertension. The bottom is below 90, not meeting the requirements for diastolic hypertension. In the past, it was always thought that diastolic hypertension, that the bottom number was most important. However, in the year 2000, most workers in the area are well aware that the top number is as important, if not more.