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GENITOURINARY TRACT DEVELOPMENT ..... . .. 33
SEXUAL DIFFERENTIATION .. . ..... ............. 38.....
DISORDERS OF SEX .... . ... . 38..........
BLADDER AND PERINEAL ABNORMALITIES ...... , ... 41
MULLERIAN ABNORMALITIES .... .. ..... ....... 41......
UTERINE FLEXION ......... , .............. , .. , ... 46
Abnormalities in the development or fusion of one or both MUllerian ducts may result in maormations which sometimes possess an obstetrical signicance. Pregnancy may be associated with anyione of these maormations, provided an ovum be cast of rom the ovaries and no serious obstacle be opposed to the upward passage of the spermatozoa and their subsequent union with it.
-]. Whitridge Williams (1903)
In females, the external genitalia, gonads, and miillerian ducts each derive from diferent primordia and in close association with the urinary tract and hindgut. Abnormal embryogenesis during this process is thought to be multifactorial and can create sporadic anomalies. Several of these can lead to infertility, subfertility, miscarriage, or preterm delivery. Thus, knowledge of genitourinary system development is essential.
• Embryology of the Urinary System
Between the 3rd and 5th gestational weeks, an elevation ofintermediate mesoderm on each side of the fetus-the urogenital ridge-begins development into the urogenital tract. Subsequently, the urogenital ridge divides into the genital ridge, destined to become the ovary, and into the nephrogenic ridge (Fig.
he nephrogenic ridges develop into the mesonephros (mesonephric kidney) and paired mesonephric ducts, also termed wolian ducts, which connect to the cloaca.
The early urinary tract develops from the mesonephros and its mesonephric ducts (Fig. 3-2A). Recall that evolution of the renal system passes sequentially through the pronephric and mesonephric stages to reach the permanent metanephric system. Between the 4th and 5th weeks, each mesonephric duct gives rise to a ureteric bud, which grows cephalad toward its respective mesonephros (Fig. 3-2B), As each bud lengthens, it induces diferentiation of the metanephros, which will become the inal kidney (Fig. 3-2C). Each mesonephros degenerates near the end of the first trimester, and without testosterone, the mesonephric ducts regress as well.