Anatomy and physiology of the pelvic floor

Abstract

Pelvic floor muscles have two important functions: they provide (1) physical support to the pelvic viscera and (2) constrictor mechanism to the anal canal, vagina, and urethra. Newer imaging and physiological studies strongly suggest that these two functions of the pelvic floor are quite distinct and are likely related to different components of the pelvic floor muscles. The pubococcygeus, iliococcygeus, and ischiococcygeus most likely provide the physical support or act as a “floor” for the pelvic viscera. On the other hand, the puborectalis muscle provides the constrictor function to the anal canal, vagina, and urethra. The urethra and anal canal, each has two constrictors or sphincters of their own. In the case of anal canal these are the IAS and EAS, and in the case of urethra they are the smooth muscle sphincter (located at the bladder neck) and rhabdosphincter (external urethral sphincter). Based on the physiologic studies, it appears that the puborectalis muscle is the third constrictor or the sphincter of anal canal. The puborectalis muscle serves as a constrictor for the urethra as well. Vagina, on the other hand, has only one constrictor mechanism, which is solely provided by the puborectalis portion or the pelvic floor muscle. We believe that puborectalis muscle is the common link between gastroenterologist, colorectal surgeon, urologist, and urogynecologist, the specialties of medicine taking care of patients with pelvic floor disorders.