MUSCULAR STRUCTURE AND DEVELOPMENT OF THE MALE POSTERIOR URETHRA

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  • 男子後部尿道筋の構造と分化についての発生学的検討
  • ダンシ コウブ ニョウ ミチスジ ノ コウゾウ ト ブンカ ニ ツイテ ノ ハ

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Abstract

The development of muscular structure of the male posterior urethra was histologically investigated serially in 5 fetuses (from 7th to 17th fetal week). The muscle structure of the male posterior urethra can be arbitrarily devided into three parts, (1) muscles of trigone and bladder neck (2) stroma of the prostate and (3) muscles in the region of the external urethral sphincter (i. e. striated urethral muscle and inframontane circular smooth muscle). Striated muscle of the urethra, which differs distinctly from other somatic striated muscles in its morphological and functional aspects, is recognizable at 8th week. They start to develop in the anterior wall of the urethra as a dense cellular accumulation, which eventually extend caudolaterally to form a horse shoe shape appearance. Striation of this muscle, however, is not noticeable until 12th week. Inframontane smooth muscle starts its differentiation between 9th and 11th week, running circularly inside of the striated urethral muscle. There is no distinct fascial plane between these two muscles which are clearly distinguishable by individual morphological difference, and instead they are intermingling each other in this area. Prostatic bud arises at 14th week and grows into prostatic mesenchyme. Following interaction between the buds and mesenchyme, prostatic smooth muscle is recognizable at 17th week around which time trigonal muscle starts its differentiation. From these observations we surmised that primitive vesical function such as emptying and holding its load must be obtained at around 8th week or 12th week at latest. Muscular development of the upper and lower urinary tract is outlined at each embryologic stage. Disturbance of this orderly process is inferred to breed various congenital urological diseases by disturbing urine transport and micturition which are deemed to be one of the essential stimulus for the development.

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