Wednesday, April 4, 2012

Components of continence mechanism in females- 1-urinary

This is presentation by Dr. Attef Soliman, many thanks to him
it discussed structural and functional components of continence mechanism in females
part1: introduction and urinary components

The anatomy of the pelvic floor includes structures responsible for active and passive support of the urethrovesical junction, vagina, and anorectum. Intrinsic and extrinsic properties of the urethrovesical neck and anorectum allow maintenance of urinary and anal continence at rest and with activity. Damage to these structures may lead to loss of support and loss of normal function of the urethra, bladder, and anorectum. 
Over time, this damage can result in isolated or combined POP and urinary incontinence support, and the system responsible for sphincteric closure 
Components of continence mechanism in female
1.  Urogenital female organs & back passage (anorectum)
  A- Urinary bladder
  B- Urethra
  C- Pelvic ureter
  D- Vagina
  E- Rectum and anal sphincters

2. Female pelvic floor

  A- Pelvic support
  B- Levator ani muscle
  C- Pelvic ligaments and fascia
  D- Connective tissues
  E- Perineal body
       F- Urogenital Diaphragm


1-Urinary Organs

A-Urinary bladder

The bladder wall musculature is often described as having three layers: inner longitudinal, middle circular and outer longitudinal. However, this layering occurs only at the BN, the remainder of the bladder musculature is composed of fibers that run in many directions, both within and between layers. 
This plexiform arrangement of detrusor muscle bundles is ideally suited to reduce all dimensions of the bladder lumen on contraction. 
The inner longitudinal layer has widely separated muscle fibers that course multidirectional. 
Near the BN, these muscle fibers assume a longitudinal pattern that is contiguous through the trigone into the inner longitudinal muscular layer of the urethra. 
The middle circular layer is prominent at the BN, where it fuses with the deep trigonal muscle, forming a muscular ring. This layer does not continue into the urethra. 
The outer longitudinal layer forms a sheet of muscle bundles around the bladder wall above the of BN. 
Anteriorly, these fibers continue past the vesical neck as the pubovesical muscles and insert into the tissues on the posterior surface of the pubic symphysis. 
The pubovesical muscles may facilitate BN opening during voiding. Posteriorly, the longitudinal fibers fuse with the deep surface of the trigonal apex and communicate with several detrusor muscle loops at the bladder base; these loops probably aid in BN closure  

The trigone has two muscular layers: superficial and deep. 

The superficial layer is directly continuous with longitudinal fibers of the distal ureter and is also continuous posteriorly with smooth muscle of the proximal urethra. 
The deep muscular layer of the trigone forms a dense and compact layer that fuses somewhat with detrusor muscle fibers. The deep layer is in direct communication with a fibromuscular sheath, Waldeyer’s sheath, in the intravesical portion of the ureter  
The deep trigonal muscle has autonomic innervation identical to that of the detrusor, being rich in cholinergic (parasympathetic) nerves and sparse in noradrenergic (sympathetic) nerves. In contrast, the superficial trigonal muscle has few cholinergic nerves, but a greater number of noradrenergic nerves  

B- Female urethra
The female urethra is a 4cm long, narrow, membranous canal that extends from the bladder to the external orifice on the vulvar vestibule 
Anatomically, the urethra can be viewed as follows: the intramural or urethrovesical junction portion has no defined support surrounding it and it rests entirely on the anterior vaginal wall and endopelvic fascia. 
In the 20th to 60th percentile of the urethra are found striated muscle, the urethral attachments to the levator muscles, and the pubovesical muscles or ligaments. Moving distally, the next 20th percentile of the urethra passes through the urogenital diaphragm and has the compressor urethral muscle and urethral sphincter muscle. The last 20th percentile is surrounded by the bulbocavernosus muscle. Female urethra is supplied by inferior vesical and long vaginal vessels and innervated by pudendal and pelvic nerves 

Several theories exist as to the role of the urethra and adjoining supportive structures in maintaining continence. 
Most of these delineate the structural support providing the urethra by the pubourethral muscles and ligaments, the anterior vaginal wall, and the endopelvic fascia attached to the arcus tendineus fascia pelvis. Moreover, most ideas stress one specific anatomic site as a primary factor assisting the continence mechanism  

Integral theory is a universal theory of function and dysfunction in the female pelvis. 
During closure, twin forward acting muscle forces (anterior ligaments); stretch the distal vagina to close the urethra from behind. 
Backward/downward muscle forces stretch the proximal vagina (and bladder base) backwards, elongating and “kinking” the proximal urethra against the anterior ligaments. 
During micturition, the forward forces relax. 
The backward/downward forces then stretch open the urethra and bladder base. 

This expands the outflow tract between midurethra and bladder base, vastly reducing resistance to flow  Continence in women is thought to be maintained by external sphincter mechanism. However, from functional point of view, it is suggested that posterior vaginal wall and levator ani muscles also contribute to the support of proximal urethra and closure of distal urethra during cough is achieved by the striated compressor urethrae and the urethrovaginal sphincter   

C-Pelvic ureter
          Intravesical ureter is about 1.5cm long and is divided into an intramural segment, totally surrounded by the bladder wall, and a submucosal segment, directly under the bladder mucosa  



atef said...

Figure 2: The component parts of the urethral support and sphincteric mechanisms. Anterior vaginal wall and its musculo fascial attachments to the pelvic diaphragm support the proximal urethra and BN. Inset, Contraction of the levator ani muscles elevates the anterior vagina and overlying BN and proximal urethra, contributing to BN closure. The sphincter urethrae, urethrovaginal sphincter, and compressor urethrae are all parts of the striated urogenital sphincter (quoted from Waters and Weber, 1999).

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