Ragionieri Luisa, Ravanetti Francesca, Gazza Ferdinando, Botti Maddalena, Ivanovska Ana, Cacchioli Antonio
Department of Veterinary Sciences, University of Parma, Parma, Italy.
J Anat. 2016 Mar;228(3):511-9. doi: 10.1111/joa.12415. Epub 2015 Nov 17.
To investigate whether the pig could be considered a suitable model to study lower urinary tract function and dysfunction, the pelvic urethra of 24 slaughtered male pigs were collected, and the associated muscles were macroscopically, histologically and histochemically analyzed. In cross-sections of the urethra, a muscular complex composed of an inner layer of smooth muscle and an outer layer of striated muscle that are not separated by fascial planes was observed. A tunica muscularis, composed of differently oriented smooth muscle bundles, is only evident in the proximal part of the pelvic urethra while, in the remaining part, it contributes to form the prostatic fibromuscular stroma. The striated urethral muscle surrounds the pelvic urethra in a horseshoe-like configuration with a dorsal longitudinal raphe, extending from the bladder neck to the central tendon of perineum. Proximally to the bladder, it is constituted of slow-twitch and fast-twitch myofibers of very small diameter, and embedded in an abundant collagen and elastic fiber net. Moving caudally it is gradually encircled and then completely substituted by larger and compact myofibers, principally presenting circular orientation and fast-twitch histochemical characteristics. So, like in humans, the cranial tract of the muscular system surrounding the pelvic urethra is principally composed of smooth musculature. The striated component cranially may have a role in blocking retrograde ejaculation, while the middle and caudal tracts may facilitate urine and semen flow, and seem especially concerned with the rapid and forceful urethral closure during active continence. Some differences in the morphology and structure between pigs and humans seem due to the different morphology of the 'secondary' sexual organs that develop from the urethral wall and to the different effect of gravity on the mechanics of the urinary system in quadruped and bipedal mammals.
为了研究猪是否可被视为研究下尿路功能及功能障碍的合适模型，收集了24头屠宰雄性猪的盆腔尿道，并对相关肌肉进行了大体、组织学和组织化学分析。在尿道横切面上，观察到由内层平滑肌和外层横纹肌组成的肌肉复合体，二者未被筋膜平面分隔。肌层由不同方向的平滑肌束组成，仅在盆腔尿道近端明显，而在其余部分则参与形成前列腺纤维肌肉基质。横纹尿道肌以马蹄形围绕盆腔尿道，有一条背侧纵向缝，从膀胱颈延伸至会阴中心腱。在膀胱近端，它由直径非常小的慢肌纤维和快肌纤维组成，并嵌入丰富的胶原纤维和弹性纤维网中。向尾侧移动时，它逐渐被更大且紧密的肌纤维包围，然后完全被替代，这些肌纤维主要呈环形排列且具有快肌组织化学特征。因此，与人类一样，围绕盆腔尿道的肌肉系统的头侧部分主要由平滑肌组织组成。头侧的横纹肌成分可能在阻止逆行射精方面起作用，而中间和尾侧部分可能促进尿液和精液流动，并且似乎特别与主动控尿时尿道的快速有力闭合有关。猪和人类在形态和结构上的一些差异似乎归因于从尿道壁发育而来的“次级”性器官的不同形态，以及重力对四足和双足哺乳动物泌尿系统力学的不同影响。
