Internal urethral sphincter

Studies on the Urinary Bladder and Internal Urethral Sphincter... 

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

Urinary tract Urinary system adverse reactions, especially enuresis, have been associated with clozapine [SED-15, 832] with an estimated incidence greater than 6%. The mechanisms include overflow incontinence after urinary retention due to the anti-muscarinic action of clozapine or a cholinomimetic activity, and reduced internal urethral sphincter tone caused by aj adrenoceptor blockade enuresis has also been attributed to a non-specific action of clozapine such as excessive sedation, lowering of the seizure threshold, and constipation exacerbating urinary retention and over-fiow. Secondary enuresis in a 21-year man with schizophrenia settled with resolution of his psychotic symptoms but later remerged after starting clozapine [SS ]. 

The bladder neck is the poorly delineated junction between the bladder and urethra at the level of the internal urethral sphincter. At the beginning of voiding the bladder floor descends and becomes funnel-shaped and in continuity with the proximal urethra. At the end of voiding, the bladder base ascends to its normal position. A wide bladder neck and a dilated proximal urethra during voiding (wide bladder neck anomaly and spinning top urethra, respectively) are variants that will be discussed in Chapter 14 on nonneurogenic bladder-sphincter dysfunction (functional disorders of the lower urinary tract). 

Fig.17.4a,b. Voiding cystourethrogram in an infant with prune belly syndrome, a High-grade reflux into the enlarged ureter b a wide bladder neck as a consequence of an open internal urethral sphincter... 

The detrusor, whose smooth muscle fibres comprise the body of the bladder, is innervated mainly by parasympathetic nerves which are excitatory and cause the muscle to contract. The internal sphincter, a concentration of smooth muscle at the bladder neck, is well developed only in the male and its principal hmction is to prevent retrograde flow of semen during ejaculation. It is rich in aj-adrenoceptors, activation of which causes contraction. There is an abvmdant supply of oestrogen receptors in the distal two-thirds of the female urethral epithelium which degenerates after the menopause causing loss of urinary control. 

---