Blood Supply The blood supply to the bladder is from the superior, middle, and inferior vesical arteries, with contribution from the uterine and vaginal vessels.
Innervation The innervation to the bladder is from the vesical plexus, with contribution from the uterovaginal plexus.
The vesical neck is the region of the bladder that receives and incorporates the urethral lumen. The female urethra is about 3 to 4 cm in length and extends from the bladder to the vestibule, traveling just anterior to the vagina.
The urethra is lined by nonkeratinized squamous epithelium that is responsive to estrogen stimulation. Within the submucosa on the dorsal surface of the urethra are the paraurethral or Skene glands, which empty through ducts into the urethral lumen. Distally, these glands empty into the vestibule on either side of the external urethral orifice. Chronic infection of Skene glands, with obstruction of their ducts and cystic dilation, is believed to be an inciting factor in the development of suburethral diverticula.
The urethra contains an inner longitudinal layer of smooth muscle and outer, circularly oriented smooth muscle fibers. The inferior fascia of the urogenital diaphragm or perineal membrane begins at the junction of the middle and distal thirds of the urethra. Proximal to the middle and distal parts of the urethra, voluntary muscle fibers derived from the urogenital diaphragm intermix with the outer layer of smooth muscle, increasing urethral resistance and contributing to continence. At the level of the urogenital diaphragm, the skeletal muscle fibers leave the wall of the urethra to form the sphincter urethrae and deep transverse perineal muscles. In the coronal plane on MRI studies, the ventral urogenital diaphragm forms an interconnected complex with the compressor urethrae, vestibular bulb, and levator ani. The dorsal part connects the levator ani and vaginal sidewall via a distinct band to the ischiopubic ramus. In the sagittal plane the parallel position of urogenital diaphragm and levator ani can be seen (27).
Blood Supply The vascular supply to the urethra is from the vesical and vaginal arteries and the internal pudendal branches.
Innervation The innervation to the urethra is from the vesical plexus and the pudendal nerve.
The lower urinary and genital tracts are intimately connected anatomically and functionally. In the midline, the bladder and proximal urethra can be dissected easily from the underlying lower uterine segment, cervix, and vagina through a loose avascular plane. The distal urethra is essentially inseparable from the vagina. Of surgical significance is the location of the bladder trigone immediately over the middle third of the vagina. Unrecognized injury to the bladder during pelvic surgery may result in development of a vesicovaginal fistula.
Dissection to the level of the trigone is rarely required, and damage to this critical area is unusual.
Figure 5.16 The rectosigmoid colon, its vascular supply, and muscular support. (Coronal view: peritoneum removed on right.) sigmoid wall broaden and fuse over the rectum to form a continuous longitudinal external layer of smooth muscle to the level of the anal canal.