Wednesday, April 4, 2012

Components of continence mechanism in females- 2-genital and back passage

This is part2 of Dr. Attef presentation about  structural and functional components of continence mechanism in females  

Part2: genital and back passage component

          The normal vaginal wall is from 2 to 3 mm thick and consists of an inner mucous coat, and outer fibrous sheath, and a muscular layer in between. 
       The inner epithelial layer is stratified squamous epithelium without glands and a fibro elastic tunica propria. 
This inner mucous membrane is surrounded by a highly developed venous plexus under autonomic and hormonal control, accounting for transudation of fluid during sexual arousal. 
Muscular coat adjacent to the inner epithelial layer is made up of smooth muscle bundles orientation allows tremendous vaginal distension, without tearing, such as occurs during parturition. The outer fibrous coat of the vagina is a dense sheath of collagen and elastic fibers. 
This CT sheath merges into the areolar CT, which joins the vagina to surrounding endopelvic fascia. Vaginal depth and axis are maintained as a result of multiple but varying muscular and ligamentous supports along the length of the vaginal wall. Laterally, fibers of vaginal fibrous layer join in strong bands of CT, which suspend the vagina and maintain its orientation within pelvis.

Although the lateral fascial support of the vagina within the pelvis is continuous and interdependent, it can be anatomically subdivided based on the segment of the vagina, from proximal to distal, supported. 

The upper level supports the apex and proximal vagina and consists of relatively long, fibrous bands arising from the greater sciatic foramen over the piriformis muscle, the pelvic bones at the sacral iliac articulation, and from the lateral sacrum. 
Its fascial support as well as the levator base-plate inferior supports in almost horizontal plane orients the upper vagina. This horizontal orientation allows the displacement of intra abdominal pressure and the downward pressure of the uterus and cervix towards the posterior vaginal wall and below it, the base plate, rather than pushing the vagina out the introitus. When this biomechanical orientation is altered postpartum or iatrogenically, such as following hysterectomy, vaginal apical eversion can occur  

The middle level of vaginal support is located at the bladder base and attaches the vagina laterally and more directly to the pelvic walls in the region of the vagina between bladder and rectum. These supporting bands are much shorter than those more proximal, near the vaginal apex. 
Mid vaginal bands join tendineus arc laterally on either side. Anteriorly, this fascia located between bladder and vagina corresponds to the pubocervical fascia, which is imbricate for anterior repair of a cystocele. 
The lower third of the vagina is in close proximity to the urethra. Here the vaginal wall attaches directly to the surrounding structures within the urogenital diaphragm. As it passes through the urogenital diaphragm, the lower third of the vagina rises almost vertically from the introitus  

Perineal ultrasound findings showed that in all women the vagina was an angulated organ. The mean angle between the upper and lower vaginal portions was 108°, in both supine and standing positions  

B-Rectum and anal sphincters

The rectum extends from its junction with the sigmoid colon to the anal orifice. The distribution of smooth muscle is typical for the intestinal tract, with inner circular and outer longitudinal layers of muscle. 
At perineal flexure of the rectum, the inner circular layer increases in thickness to form the internal sphincter. 
The internal anal sphincter is under autonomic control (sympathetic and parasympathetic) and is responsible for 85% of the resting anal pressure. 
The outer longitudinal layer of smooth muscle becomes concentrated on the anterior and posterior walls of the rectum, with connection to the perineal body and coccyx, and then passes inferiorly on both sides of the external anal sphincter. 
The external anal sphincter is composed of striated muscle that is tonically contracted most of the time and can also be voluntarily contracted. 
Various divisions of the external anal sphincter have been described, and although there is no consensus, recent descriptions favor superficial (combining the previous superficial and subcutaneous components) and deep components. The external anal sphincter functions as a unit with the puborectalis portion of the levator ani muscle group. 
The anal sphincter mechanism comprises the internal anal sphincter, the external anal sphincter, and puborectalis muscle. As with the BN and urethra, a spinal reflex causes the striated sphincter to contract during sudden increases in intra abdominal pressure, such as coughing. The anal-rectal angle is produced by the anterior pull of the puborectalis muscles. These muscles form a sling posteriorly around the anorectal junction   



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