Development of the renal system

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Development of the renal system


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Development of the renal system

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USMLE® Step 1 style questions USMLE

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A group of researchers are studying the effects of an antihypertensive medication during pregnancy. Follow-up studies demonstrate that the medication adversely affects the differentiation of the ureteric bud into its direct derivative in a developing embryo. Development of which of the following renal structures will be affected in the exposed fetus?  


The renal system starts developing during week 4 of intrauterine life.

At this point, the embryo is made up of three primitive germ layers: the ectoderm, the mesoderm and the endoderm.

The mesoderm also has three parts: the paraxial mesoderm, which flanks the embryo’s future vertebral column; the intermediate mesoderm, which is just lateral to the paraxial mesoderm; and the lateral plate mesoderm, which is the most lateral of all.

The intermediate mesoderm on either side of the embryo condenses to form a cylindrical structure called the urogenital ridge.

This ridge runs parallel to the embryo’s future vertebral column, and it gives rise to both the urinary and genital systems.

The portion of the urogenital ridge called the nephrogenic cord develops into the urinary structures.

Now, during the development of the urinary system, there are three sets of structures that emerge from the nephrogenic cord, and they form in a craniocaudal fashion—from head to tail-end.

The first structure to emerge from the nephrogenic cord is the pronephros, which appears in the neck region of the embryo at the beginning of week 4.

The pronephros consists of the pronephric duct and the nephrotomes in front of it.

The pronephric duct is basically a pipe that runs down the length of the nephrogenic cord, and the nephrotomes are small chunks of tissue that break off from the nephrogenic cord.

However, the pronephros doesn’t produce urine, and regresses by the end of week 4.

Before the pronephros completely disappears, a second set of structures called the mesonephros appears in the thoracic and upper lumbar region of the nephrogenic cord.


The renal system starts to form at about week 4 of gestation from a portion of the urogenital ridge called the nephrogenic cord. The nephrogenic cord gives rise to three overlapping developmental stages: the pronephros, the mesonephros, and the metanephros. Pronephros consists of an early and nonfunctional system, which regresses by week 4. Next is the mesonephros, which functions as a primitive excretory system in the embryo. Most tubules regress by week eight and are replaced by the metanephros. Metanephros give rise to actual kidneys, which appear at around week five, and become mature enough to secrete urine around week ten.


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