Age Related Anatomical and Functional Characteristics of Human Kidney

Development of the human kidney begins at the end of the first month, and the kidney becomes functional in the course of the second month of antenatal life. In the last trimester, the fetal kidney already manifests first involutive changes. From then on to its adult maturity, the kidney is characterised by intensive processes of maturation, but also evident involutive changes. The dynamism of these changes, however, is different in certain life ages. The antenatal period is characterised by intensive processes of nephrogenesis, realised in three successive phases of renal development: pronephros, mesonephros, and metanephros. The first two changes represent a temporary system, while the third stands for a permanent system of excretion, that is, a definitive kidney. The functioning of kidneys, though not necessary in the antenatal stadium, indicates their excretory, homeostatic and endocrine roles, and signifies the maturation process. After birth, there is a further process of structural and functional maturation of the kidneys. With a definitive number of nephrones at birth, renal mass increases at the expense of growth of certain nephrone structures and interstitium. The kidney reaches its full anatomical and functional maturity by the end of the third decade of life. From then on, the kidney is characterised by involutive changes of varying intensity. By the end of the sixth decade these changes are slow; afterwards, to the end of life, they show a trend of very rapid progression, and are a consequence primarily of the reduced renal perfusion. In spite of that, under normal conditions they do not show signs of renal insufficiency even in a well-advanced age. The involutive renal changes can be separate, but they can coincide with corresponding renal diseases. In some individuals this can result in a progressive failure of renal functions in an advanced age.