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KMID : 1237720120450020079
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Anatomy & Cell Biology
2012 Volume.45 No. 2 p.79 ~ p.85
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Reappraisal of intergender differences in the urethral striated sphincter explains why a completely circular arrangement is difficult in females: a histological study using human fetuses
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Masumoto Hiroshi
Takenaka Atsushi
Rodriguez-Vazquez Jose Francisco
Murakami Gen
Matsubara Akio
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Abstract
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To investigate why the development of a completely circular striated sphincter is so rare, we examined histological sections of 11 female and 11 male mid-term human fetuses. In male fetuses, the striated muscle initially extended in the frontal, rather than in the horizontal plane. However, a knee-like portion was absent in the female fetal urethra because, on the inferior side of the vaginal end, a wide groove for the future vestibule opened inferiorly. Accordingly, it was difficult for the developing striated muscle to surround the groove, even though there was not a great difference in width or thickness between the female vestibule and the male urethra. The development of a completely circular striated sphincter seems to be impossible in females because of interruption of the frontal plane by the groove-like vestibule. However, we cannot rule out the possibility that before descent of the vagina, the urethral striated muscle extends posteriorly.
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KEYWORD
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Urethal rhabdosphincter, Genital tract, Urogenital sinus, Colliculus, Human fetus
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