Description

The mature kidneys are end organs, which means the arteries supplying the renal tissue are end arteries which do not anastomose. Therefore, on occlusion of one of the branches, the tissue supplied by it will become necrotic. There is no post-natal nephrogenesis. The weight and volume of the kidney decreases by 20% between the age of 30 – 80 years: the combined weight of the kidneys falls from between 270 grammes in young adulthood to approximately 180 grammes at the age of 80. The loss of renal mass is primarily cortical with relative sparing of the renal medulla. The total number of glomeruli decreases with age by 30 – 50% with an increasing number of sclerotic/hyalinized and non-functioning glomeruli. The renal tubules decrease in number and distal tubules develop diverticular which often contain bacteria and may result in pyelonephritis. Changes also occur in the intra-renal vasculature with age. There are variable sclerotic changes in the wall of larger renal vessels but small vessels are spared with ageing. There are also two distinctive patterns of change in the arteriolar-glomerular unit. In one type collapse of the glomerular tuft is associated with obliteration of preglomerular arterioles and loss in blood flow. The second pattern, seen primarily in the juxtomedullary area, is direct anatomical shunting of blood flow in the cortex between afferent to efferent arterioles as a result of glomerular loss.