External urethral sphincter

Two types of urinary tract symptoms are commonly seen in MS incomplete bladder emptying and incontinence. Incomplete bladder emptying is due to dyscoordination of the external urethral sphincter and detrusor activity.14 Most patients who develop this condition require intermittent or permanent uri-I nary catheterization.14 Incontinence in most MS patients is... 

The urethral sphincter, a combination of smooth and striated muscles within and external to the urethra, maintains adequate resistance to the flow of urine from the bladder until voluntary voiding is initiated. Normal bladder emptying occurs with opening of the urethra concomitant with a volitional bladder contraction. 

Duloxetine, a dual inhibitor of serotonin and norepinephrine reuptake indicated for depression and painful diabetic neuropathy, is expected to become first-line therapy for SUI. Duloxetine is thought to facilitate the bladder-to-sympathetic reflex pathway, increasing urethral and external urethral sphincter muscle tone during the storage phase. 

Einally, external urethral sphincter (voluntary sphincter, or rhabdosphincter) is a striated circumscribing structure emanating from the bladder neck and bladder base detrusor through the mid-urethra in the female and intermediate prostatic urethra in the male. While also surrounding Cowper s glands in the male, these rhabdosphincter subunits contract, most likely, only with ejaculation (Hutch, 1972 Elbadawi, 1980), along with simultaneous anal rhabdosphincter, bulbo-cavernosus muscle, and cremaster muscle contractions. 

External urethral sphincter muscle probably has cholinergic and adrenergic autonomic innervation as well as cholinergic striated muscle innervation (Elbadawi and Schenk, 1974). This rhabdosphincter is unique when compared to other striated muscle in that it has a higher density of neural end-plates as well as blood vessel-independent neural plexuses. Efferent rhabdosphincter innervation is probably via the pudendal nerve while the lissosphincter efferents probably emanate from the pelvic plexus (Elbadawi and Schenk, 1974). 

Elbadawi, A. and Schenk, E.A. (1974) A new theory of the innervation of bladder musculature. 4. Innervation of the vesicourethral junction and external urethral sphincter./ Urol 111 613-615. 

Conte et al. (1991) proposed a method for simultaneous recording of vesical and the external urethral sphincter pressure in urethane-anesthetized rats. 

In some studies, denervation of the external urethral sphincter was performed (Somma et al. 1989 Parlani et al. 1992). Rats were anesthetized with 30 mg/kg penthotal i.p., then the major pelvic ganglia, known to provide both sympathetic and parasympathetic innervation to the urinary bladder and the external urethral sphincter (Hulsebosh and Goggeshall 1982 Purinton et al. 1973 Watanabe and Yamamoto 1979) are isolated and bilaterally removed through a small incision of the lower abdomen. 

In the same preparations, somatic denervation of the external urethral sphincter was obtained by cutting the pudendal nerves. The paravertebral muscles were care-... 

Parlani M, Manzini S, Argentino-Storino A, Conte B (1992) The rat external urethral sphincter. An in vitro model to evaluate the activity of drugs on the smooth and striated components of the urinary bladder outlet. J Pharmacol Toxicol Meth 28 85-90... 

Dense connective tissue between external urethral sphincter (and transverse perineal muscle in male) and pubic bone... 

Fig. l.lla,b. External urethral sphincter (asterisks), a Axial section (400 pm) of a 24-week-old female fetus, embedded in the transverse perineal membrane. x9. b Computer-assisted three-dimensional reconstruction of a female fetus, p o, pubic bone u, urethra... 

Fig. 1.11 a) and the external urethral sphincter. As has been reported previously [37], this muscle is horse-shoe- or omega-shaped during fetal development and incompletely covers the urethra (Fig. 1.11). The dorsal ends of this muscle are connected by a plate of dense connective tissue that is small in the female where it is firmly attached to the ventral wall of the vagina (Figs. l.lOd, 1.11a). Whereas most of the fibers of the external urethral sphincter run semicircular, the most caudal fibers nearly run in a transverse plane. This portion predominates in the male and therefore has been considered as the male s deep transverse perineal muscle. However, it does not exist in the female [42].

Ludwikowski B, Oesch-Hayward I, Brenner E, Fritsch H (2001) The development of the external urethral sphincter in hmnans. BJU International 87 565-568... 

Stenoses caused by the use of instruments (catheterization, endoscopic resection) are usually located in three areas the external meatus, suspensor ligament of the penis and just below the urethral sphincter (Blaivas and Norlen 1984). 

Hoebeke et al. (2001) in a publication about 1,000 videourodynamic studies in children with nonneurogenic bladder dysfunction found urge syndrome (overactive bladder or unstable bladder) in 58% (male female ratio 58 42), dysfunctional voiding (overactivity of the external urethral sphincter) in 32% (male female ratio 49 51) and lazy bladder in 4% (male female ratio 20 80). Furthermore, he found that the age distribution provided evidence against a dysfunction sequence as mentioned above. 

By the age of 4-5 years many children have been toilet-trained successfully and have adopted an adult pattern of urinary control. This is also characterized by the absence of involuntary or uninhibited detrusor contractions during bladder fiUing. Even if the bladder is full and there is a strong desire to void, no bladder contractions will occur. With micturition, coordinated relaxation of the external urethral sphincter takes place. Therefore, bladder emptying is under low intravesical pressure in children and adults. 

The child, attempting to maintain continence during such contractions, must voluntarily and tightly constrict the external urethral sphincter to stay dry. This results in simultaneous and unphysi-ological contraction of both the bladder and external urethral sphincter. During this event functional urinary obstruction and high intravesical pressure... 

Fig. 14.2a-c. Male, 2 months old moderate bilateral fetal hydronephrosis, VCU. Reduced bladder filling volume (20 ml) residual urine early uninhibited detrusor contractions transformed into premature micturition, a Minor bladder trabecu-lation, short phase of normal micturition. b,c Dyscoordinated voiding, contraction of external urethral sphincter dilated posterior urethra, male spinning top urethra... 

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