Distribution Of The Female Human Urethral Sphincter: Immunohistochemical Studies In The Fetus.

Objective: The precise nature,quantity and location of nerve fibers innervating the female urethral sphincter have not been clearly established. Classical anatomical studies based on cadaver dissections have provided conflicting results concerning the location of pudendal and autonomic nerve fibers. This study was designed to identify nerve fibers innervating the urethral sphincter through immunohistochemical analysis relations in the female human fetus.Methods: Urethras of 12 normal female human fetuses between 21 and 40 weeks of gestation were treated by paraffin embedded with choline acetylcatransferase (CHAT) and neuropeptide Y (NPY) SP immunohistochemical staining. The staining results were analyzed quantitatively and semiquantitatively statistically.Results: From the urethra internal orifice to external orifice, the positive region of NPY became smaller and the density thinner, there was markedly significant difference between the proximal third and the distal third, the middle third and the distal third(P＜0.01), but there was no significant difference between the proximal third and the middle third. The positive region of CHAT was mainly located in the middle part of urethra, the proximal secondly, there was statistically significant difference between them(P＜0.01).Conclusion: 1. The positive regions of choline acetylcatransferase (CHAT) and neuropeptide Y (NPY) immunohistochemical staining located at the middle third mainly, there were statistically significant difference between them. It was the location of the neural transmitters of cholinergic nerves and adrenergic nerves; 2. Striated sphincter muscle beginned at the distal position of the proximal third of the urethra, it located at the outside of the smooth muscle and became thick grandually to the distant end. Its pinnacle was the middle third, then it became thinner and thinner; 3. In the middle third of the urethra of female human fetuse, there was no obvious difference between the smooth and striated sphincter, it could be seen clearly that their fibres interveined each other and transitted grandually. The alleged urethral sphincter complex had come into being.The immunohistochemical staining of choline acetylcatransferase and neuropeptide Y in the anatomical structures of the urethral sphincter provides a better understanding of the origin and nature of the innervation participating in urinary continence. They have conductive significance for clinical practice.