Ludwikowski B, Oesch Hayward I, Brenner E, Fritsch H
Department of Paediatric Surgery, Landeskliniken, Salzburg, Austria.
BJU Int. 2001 Apr;87(6):565-8. doi: 10.1046/j.1464-410x.2001.00086.x.
To assess the hypothesis that during fetal development, the external urethral sphincter changes from a concentric sphincter of undifferentiated muscle fibres to a transient ring of striated muscle which regresses caudo-cranially in the posterior urethra during the first year of life, when the sphincter assumes its omega-shaped configuration.
The anatomy and development of the external urinary sphincter was assessed in human males and females during fetal life. Plastic-embedded sections (transverse, sagittal and frontal planes; 300-700 microm) of the pelvis of 31 females and 31 males (9 weeks of gestation to newborn) were stained with azure II/methylene blue/basic fuchsin and viewed at x 4-80. The sections of interest were taken from the bladder neck to the perineum. The sections of the membranous urethra were reconstructed three-dimensionally using a computer program.
In both male and female an omega-shaped external sphincter was apparent in all specimens at > 10 weeks of gestation. In the early fetal period (ninth week), there was undifferentiated mesenchyme; in this period the mesenchyme was more dense in the anterior part and loose in the posterior part of the urethra. In females, there was a close connection between the urethra and the anterior wall of the vagina.
The omega-shaped configuration of the external urethral sphincter was recognisable from 10 weeks of gestation in both sexes. There was no suggestion of a change from a cylindrical to an omega-shaped sphincter in the fetal period to birth. Also, a transient 'tail' posterior to the sphincter was not apparent. The rectovesical septum was well developed in neonates. There is no reason to assume that the development of the septum leads to an apoptosis of muscle cells in the posterior part of the external sphincter in males after birth. The anatomical development of the external sphincter does not explain transient outlet obstruction during fetal life. The function of the muscle may change during development because of neuronal maturation.
评估以下假说：在胎儿发育过程中，尿道外括约肌从由未分化肌纤维组成的同心括约肌转变为横纹肌的短暂环状结构，在生命的第一年，当括约肌呈现其ω形结构时，该环状结构在尿道后部向尾侧至头侧退缩。
在胎儿期评估人类男性和女性尿道外括约肌的解剖结构和发育情况。对31名女性和31名男性（妊娠9周直至新生儿）骨盆的塑料包埋切片（横切面、矢状面和额状面；300 - 700微米）用天青II/亚甲蓝/碱性品红染色，并在4 - 80倍显微镜下观察。感兴趣的切片取自膀胱颈至会阴。使用计算机程序对膜性尿道的切片进行三维重建。
在妊娠10周以上的所有标本中，男性和女性均可见ω形的外括约肌。在胎儿早期（第9周），存在未分化的间充质；在此期间，尿道前部的间充质更致密，后部则疏松。在女性中，尿道与阴道前壁之间有紧密连接。
妊娠10周起，两性的尿道外括约肌均可辨认出ω形结构。在胎儿期至出生期间，没有迹象表明括约肌从圆柱形转变为ω形。此外，括约肌后方也没有明显的短暂“尾巴 ”。新生儿的直肠膀胱隔发育良好。没有理由认为该隔的发育会导致男性出生后尿道外括约肌后部的肌肉细胞凋亡。尿道外括约肌的解剖发育并不能解释胎儿期短暂的出口梗阻。由于神经元成熟，肌肉的功能可能在发育过程中发生变化。
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