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Renal development is characterized by proliferation, migration, induction and cell differentiation. It is a process that takes a long time and is subject to topographic changes. This explains the higher incidence for abnormalities of the kidneys or the urinary tract in human pathology. In approximately 3 - 4% of the population one finds abnormalities of the urinary tract. Many remain asymptomatic or are discovered in advanced age. A certain number of urinary tract abnormalities, though, can already be diagnosed in the fetus in utero using ultrasound. The kidneys and the bladder can already be discerned after the 12th week, but in this early stage, great care needs to be taken to discover such abnormalities. A disorder in the formation or the excretion of urine has large effects on the development of the fetus. It leads to an oligohydramnios (insufficient quantity of amniotic fluid), which is seen clinically in the Potter sequence.
Basically, one distinguishes between abnormalities of the kidneys and those of the urinary tract, even though the disorder of one of the components causes a whole series of further disorders of the entire kidney-urinary system to take place. This is due to the reciprocal induction of the ureter anlage and the metanephric blastema. The cause of most renal abnormalities is not known and one only barely understands the molecular foundations, except chromosomal aberrations and a few genetically transmitted diseases (e.g., polycystic kidneys).
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