Yy

External striated muscle

Longitudinal & circular smooth muscle

Lamina propria

Urethral mucosa

Figure 4-1.5. A transverse section through the mid portion of the female urethra.The female urethra is composed of an infolding epithelium, a fibromuscular envelope of spongy tissue,a middle smooth muscle,and an outer skeletal muscle layer. (Reprinted with the permission of The Cleveland Clinic Foundation.)

empty through two small ducts on either side of the external urethral meatus.

Histologically, the female urethra is composed of an infolding epithelium, a fibromuscular envelope of spongy tissue, a middle smooth muscle, and an outer skeletal muscle layer (Figure 4-1.5). The urethral mucosa is thrown into folds, allowing for a mucosal to mucosal coaptation. This forms a seal similar to a washer on a sink and is one of several mechanisms of continence. Under the mucosa is the lamina propria, which contains a rich vascular spongy tissue. This layer, when congested, constricts the mucosal lining enhancing mucosal coaptation. The smooth muscle of the urethra consists of longitudinal fibers, which emanate from the internal longitudinal fibers of the bladder. The outer semicircular smooth muscle fibers arise from the outer longitudinal layer of the bladder. Both sets of smooth muscle start at the bladder neck and extend to the distal urethra, where they end in a fibrous ring. The outer semicircular smooth muscle is more prominent in the mid urethra, where the smooth muscle fibers mix with the striated fibers of the external urethral sphincter. Both smooth muscle layers become sparse in the distal urethra. Constriction of these muscles extenuates the mucosal to mucosal coaptation. Collagen forms a major component, and elastin a minor component of the urethral smooth muscle layers. Collagen is thought to be a contributor to passive closure of the urethra, whereas elastic fibers are thought to prevent overdistention of the urethra.

DeLancey4 has described the relationship of the paraurethral structures in the female. The location of these structures were described as a percentile of total urethral length, with the zero percentile defined as the internal urethral meatus and the 100 th percentile as the external urethral meatus. The rationale for this scheme is that urethral length can vary, and there is no exact and reproducible length where these structures exist along the urethra from person to person. Instead, the periurethral muscles tend to lie in regions of the urethra as a percentile of its total length. The internal urethral meatus is the zero percentile. At the level of the bladder neck, the urethra passes through the wall of the bladder. The end of the bladder wall constitutes the 15th percentile of the urethra. At this level, the striated urethral sphincter muscle surrounds the urethra and extends from the 18th to the 64th percentile. At the 54th percentile, the urogenital diaphragm, the compressor urethrae and the urethrovaginal sphincter are encountered and extend to the 76th percentile (Figure 4-1.6). These periurethral muscles are continuous with the striated sphincter. The urethral compressor originates from the ischial tuberosity and extends over the urethra to the opposite tuberosity. The transverse vaginal muscle is a thin sheet, which is characterized as part of the compressor that lies below the urethra, filling the space between the urethra and the urethrovaginal sphincter. The urethrovaginal sphincter is flat and merges on the ventral side of the urethra with the urethral compressor, and extends along the sides of the urethra and vagina to enclose them in a circular manner. The pubococcygeus muscle is the most medial portion of the levator musculature and runs from the pubis to the coccyx. It is positioned on the lateral side-wall of the vagina and urethra. When this muscle contracts, it provides some urethral compression; however, it is not considered a true sphincter muscle. The point of maximal urethral pressure at rest in the supine position correlates to this area of muscle described. The maximum

Urethra

Vagina

Pubococcygeus muscle

Pubococcygeus muscle

Vagina

Transverse vaginal muscle

Figure 4-1.6. Periurethral muscles. (Reprinted with the permission of The Cleveland Clinic Foundation.)

Transverse vaginal muscle

Figure 4-1.6. Periurethral muscles. (Reprinted with the permission of The Cleveland Clinic Foundation.)

voluntary increase in urethral pressure also correlates to this area. From the 79th to the 100th percentile of the urethra, the bulbocavernosus and ischiocavernosus muscles lie adjacent to, but do not connect to, the urethra. These muscles do not contribute to continence. The remaining urethra is composed of fibrous tissue and does not have a significant muscular component. This tissue is derived from the subcutaneous tissue and suspensory ligament of the clitoris. Between the 20th and 60th percentile of the urethra, the pubourethral ligament and the vaginol-evator run anteriorly from the urethra and vaginal wall, respectively, to attach to the pelvic wall. The pubourethral ligament connects the urethra to the pubis and the vagi-nolevator connects the vagina to the pubococcygeus portion of the levator ani muscle. Fibrous tissue and muscle make up these structures. It has been implied that the support and compression of the urethra on a hammock of vaginal tissue causes compression of the urethra with Valsalva. This is thought to be one of many contributors to continence.

The urethral arterial blood supply arises from the inferior vesical arteries at the bladder neck, as well as the vaginal branches of the internal iliac vessels. The urethra's venous drainage originates from the inferior, middle, and superior vesicular veins, as well as the clitoral plexus.

Constipation Prescription

Constipation Prescription

Did you ever think feeling angry and irritable could be a symptom of constipation? A horrible fullness and pressing sharp pains against the bladders can’t help but affect your mood. Sometimes you just want everyone to leave you alone and sleep to escape the pain. It is virtually impossible to be constipated and keep a sunny disposition. Follow the steps in this guide to alleviate constipation and lead a happier healthy life.

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