Renal agenesis

Alright, so renal agenesis—genesis is the origin or formation of something, and the prefix a means not, and renal refers to the kidneys, so renal agenesis is when the kidneys don’t form. Since there are two kidneys, renal agenesis can refer to just one kidney not developing, called unilateral renal agenesis, or URA, or neither kidney developing, called bilateral renal agenesis, or BRA.

Alright so during fetal development, first off, you’ve got this structure called the mesonephric duct which is involved in development of urinary and reproductive organs, and during the 5th week of gestation, a little guy called the ureteric bud starts pushing its way into another structure called the metanephric blastema, and together, these two little embryologic structures go on to develop into a kidney. At about the 7th week, nephrogenesis, or formation of the kidneys, starts under the influence of that ureteric bud.

By about 20 weeks, the ureteric bud has formed the ureters, the renal calyces, collecting ducts, and collecting tubules, while the metanephric blastema develops into the nephron itself, which includes the epithelial cells and the podocytes of the Bowman’s capsule.

In the third trimester and throughout infancy, the kidneys continue to grow and mature.

With renal agenesis, the ureteric bud fails to induce development of the metanephric blastema, and so either one or both kidneys don’t develop. Although not completely known, it’s thought that this is a result of a combination of genetic as well as in utero environmental factors like toxins and infections.

Newborns with unilateral renal agenesis are usually asymptomatic if the other kidney’s otherwise healthy. Now that one kidney’s doing all the filtering, though, over time unilateral renal agenesis can lead to hypertrophy, or growth of the kidney, which later in life can increase the risk of hypertension as well as renal failure.

Alright so let’s move to bilateral agenesis, which is where there are no kidneys. Normally, as the kidneys start to function around week 16, they start to filter the fetal blood, which means that some fetal urine gets produced, some of which contributes to the amniotic fluid that the fetus floats around in.