Liu Tong, Muro Satoru, Tharnmanularp Suthasinee, Akita Keiichi
Department of Clinical Anatomy, Tokyo Medical and Dental University (TMDU), 1-5-45 Yushima, Bunkyo-Ku, Tokyo, 113-8510, Japan.
Princess Srisavangavadhana College of Medicine, Chulabhorn Royal Academy, Bangkok, Thailand.
Int Urogynecol J. 2025 Mar;36(3):647-654. doi: 10.1007/s00192-025-06045-w. Epub 2025 Jan 20.
The urethra is surrounded by layers of smooth muscle, including inner longitudinal and outer circler muscles, as well as the skeletal muscle of the external urethral sphincter. However, the extent of these muscles and their relationship with the levator ani (LA) remain unclear. This study aimed to clarify the composition of muscle layers around the female urethra and their three-dimensional arrangements.
Pelvises from five female cadavers were collected for histological analysis. The surrounding urethral tissue was serially sectioned and stained with Elastica van Gieson stain to identify the connective and muscular tissues. Immunohistological staining with an anti-smooth muscle antibody was performed to confirm the distribution of the smooth and skeletal muscles. Thereafter, muscle layers were three-dimensionally reconstructed on the basis of serial histological sections.
The female urethra was surrounded by four muscle layers arranged from inner to outer layers in the following order: longitudinal smooth muscle, circular smooth muscle, the external urethral sphincter (EUS), and an outermost smooth muscle layer. These muscles surrounded the urethra and partially extended anteriorly. Moreover, smooth muscle fibers extending from the vagina were found between the LA and EUS.
This study clarified the distribution of muscle tissue surrounding the female urethra, showing that the EUS is connected to the LA through the outermost smooth muscle layer. Thus, urination control likely involves both the urethral muscle layers and the pelvic floor muscles.
尿道被多层平滑肌所环绕，包括内层纵行肌和外层环行肌，以及尿道外括约肌的骨骼肌。然而，这些肌肉的范围及其与肛提肌（LA）的关系仍不清楚。本研究旨在阐明女性尿道周围肌层的组成及其三维排列。
收集五具女性尸体的骨盆进行组织学分析。对尿道周围组织进行连续切片，并用弹性纤维番红染色以识别结缔组织和肌肉组织。用抗平滑肌抗体进行免疫组织化学染色以确认平滑肌和骨骼肌的分布。此后，基于连续组织学切片对肌层进行三维重建。
女性尿道被四层肌层所环绕，从内层到外层依次为：纵行平滑肌、环行平滑肌、尿道外括约肌（EUS）和最外层平滑肌层。这些肌肉围绕尿道并部分向前延伸。此外，在LA和EUS之间发现了从阴道延伸而来的平滑肌纤维。
本研究阐明了女性尿道周围肌肉组织的分布，表明EUS通过最外层平滑肌层与LA相连。因此，排尿控制可能涉及尿道肌层和盆底肌。
