This article will serve as a brief overview of the development of the urogenital system, a critical process of development occurring from 1-20 weeks of human development.
Urogenital development plays an essential role in human function and reproduction; consequently, malfunction or maldevelopment of this system may result in profound deleterious effects on fertility, urinary continence, and renal function. During week one to week 6, the human embryo is sexually indifferent; genetically male and female embryos are phenotypically alike, both expressing mesonephric (Wolffian) ducts. Around week 7 of development, sexual differentiation begins and continues until the sex, based on the external genitalia, of an embryo can be fully distinguished around week 12, and further phenotypic differentiation completes near week 20—the driving force for this phenotypic differentiation between females and males is primarily hormonal influence.
The urogenital system arises from the intermediate mesenchymal tissue (intermediate mesoderm forms kidneys and ureters) and forms the urogenital ridge on both sides of the aorta.
Development of the urogenital ridge begins with three sets of tubular nephric structures, from cranial to caudal: pronephros, mesonephros, and the metanephros.
Metanephric Blastema - Derivatives
Ureteric Bud - Derivatives
Steps in Renogensis
The urethra is a part of the urogenital system, urethra develops from the endoderm of the urogenital sinus. The urethra runs from the neck of the urinary bladder to the external urethra orifice. The male urethra divides into four parts prostatic, membranous, bulbar, and penile part.
Some Potential Malformations that may occur with errors during development:
Female is the default phenotypic differentiation. Degeneration of the mesonephric duct occurs, allowing for the paramesonephric duct to develop.
In males, the SRY gene on the Y chromosome is what produces the testis-determining factor, which allows for the development of the testes. As a result, testes then can give rise to Sertoli cells, which produce: Mullerian inhibitory factor (MIF), which suppresses the development of paramesonephric ducts, and Leydig cells, which produce the androgens that are necessary for the development of the mesonephric ducts.
Male and female genital homologs:
The penis develops from ambisexual genital tubercle during early embryo development (8-18 weeks of gestation) under androgen influence. The absence of androgen leads to the development of the female genital tubercle, which will then develop into the clitoris, which is homologous with the penis except for the "clitoral urethra." It has been shown that the urethra of the penis develops via an "opening zipper" by canalization of the solid urethral plate to form the open urethral groove.
Females undergo the same process of canalization, forming the open vestibular groove. The "closing zipper" or epithelial fusion of the urethral folds in males occurs within the shaft of the penis and leads to the formation of the urethra. The "closing zipper" does not happen in females since it occurs under androgenic stimulation, which is absent secondary to the absence of testes.
Development of external genitals occurs by three main pathways:
The most common malformations sonographically identified during the prenatal period are congenital abnormalities of the urinary tract and kidneys, with obstructive uropathies being the most common. From 9 to 12 months of pregnancy, the fetal kidneys can be visualized on both sides of the lumbar spine and are easy to see because of their hyperechogenicity during the first trimester.
Color Doppler can make it even easier to identify both renal arteries. Fetal urine production begins at nine weeks gestation, increasing significantly beyond 16 weeks, at 20 weeks, nearly 90% of amniotic fluid is urine produced by the fetus. The fetal bladder can be visualized from 13 weeks onward. From 15 weeks onwards, visualizing the urogenital system via ultrasound becomes easier due to ongoing differentiation.
It is vital to diagnose abnormalities during the prenatal period and treat any critical obstructions or urinary tract infections (UTIs) for the best potential outcome of the affected child. After diagnosis with prenatal ultrasound, about 60% of affected children have surgery for either urinary tract or renal problems in their first five years of life.
A routine fetal ultrasound of the urogenital tract consists of the assessment for the size, location, and presence of both kidneys and bladder, along with the evaluation of their structure and echogenicity, as well as the development of the external genitalia and amniotic fluid quantity.
In-depth and thorough knowledge regarding embryological origin and evolution into adulthood is important in the understanding of the pathophysiology of congenital and acquired anomalies. This knowledge enables clinicians to initiate the treatment options that are most appropriate for the patient. The integration of embryology in the medical curriculum is essential for better patient outcomes.
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