A. Hypertensive Arteriosclerosis
Prolonged hypertension causes the walls of the affected arteries to become firmer and thicker, and the lumen are often wider than normal. Arteries appear to be generally enlarged and they may become somewhat tortuous. These changes can be seen especially in the retinal arteries (hypertensive retinopathy), kidneys, pancreas, and other organs. The lumen of minute arterial branches, however, are often diminished owing to thickening of the intima.
Microscopic examination shows that the arterial wall is generally thickened with a proliferation of connec¬tive tissue cells and formation of new tissue both in the intima and the media. There is a considerable amount of concentric fibrous thickening, often without atheroma formation. In the thickening of media there may be distinct evidence of muscular increase, but in most cases the muscle fibers are found to be undergoing replacement by fibrous tissue leading to distinct fibrosis of the media. There is, however, true muscular hypertrophy. In young subjects with severe kidney disease and severe hyperten¬sion, hypertrophy of the media occurs before secondary fibrosis has appeared. This hypertrophy is similar to hypertrophy of the myocardium in response to the increased workload imposed by the high pressures. In the thickened intima, there is distinct hypertrophy and hyperplasia of the longitudinal muscle layer next to the internal elastic lamina. A reactive increase in the support¬ing elements of the vessel wall occurs in both muscle and elastic tissue. This occurs in response to increased blood pressure. This type of musculoelastic hyperplasia can be arrested by some antihypertensive agents.

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