Urethra, structure

This chapter discusses drug s used to treat urinary tract infections (UTIs) and certain miscellaneous drag > used to relieve the symptoms associated with an overactive bladder (involuntary contractions of the detrusor or bladder muscle). Structures of the urinary system that may be affected include the bladder (cystitis), prostate gland (prostatitis), the kidney, or the urethra (see Pig. 47-1). These drug s also help control the discomfort associated with irritation of the lower urinary tract mucosa caused by infection, trauma, surgery, and endoscopic procedures. 

Urinary tract infection (UTI) is an infection caused by pathogenic microorganisms of one or more structures of the urinary tract. The most common structure affected is the bladder, with the urethra, prostate, and kidney also affected (see Pig. 47-1). Display 47-1 identifies the disorder most frequently associated with each of these structures within the urinary system. Clinical manifestations of a UTI of the bladder (cystitis) include urgency, frequency, burning and pain on urination, and pain caused by spasm in the region of the bladder and the suprapubic area. 

Urinary incontinence can result from abnormalities within (intrinsic to) and outside of (extrinsic to) the urinary tract. Within the urinary tract, abnormalities may occur in the urethra (including the bladder outlet and urinary sphincters), the bladder, or a combination of both structures. Focusing on abnormalities in these two structures, a simple classification scheme emerges for all but the rarest intrinsic causes of UI. Accurate diagnosis and classification of UI type is critical to the selection of appropriate drug therapy. 

The goal of treatment of SUI is to improve urethral closure by stimulating a-adrenergic receptors in the smooth muscle of the bladder neck and proximal urethra, enhancing supportive structures underlying the urethral epithelium, or enhancing serotonin and norepinephrine effects in the micturition reflex pathways. 

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. 

The structure of the bladder, ureter, and urethra are similar in that they contain three layers, the mucosa, muscularis, and serosa. In the bladder (Figure 3.16) the inner layer (mucosa) when empty is infolded and it is made up of transitional epithelium. The lamina propria that is found below contains collagen and elastic fibers in the deeper layer. The muscularis is prominent and contains muscle fibers that are arranged in branching bundles separated by connective tissue. Muscular contraction causes expulsion of fluid from the bladder into the ureter. The connective tissue between the muscle fiber bundles merges with the connective tissue of the serosa. The serosa is continuous with the peritoneal lining. 

FIGURE 1 Female reproductive system and related structures vagina (1), cervix (2), uterus (3), ovary (4), fallopian tube (5), urinary bladder (6), urethra (7), anus (8), rectum (9), colon (10), vestibule (11), and pubic symphysis (12). (Courtesy of Lufs Pauperio.)... 

Lower tract infections include cystitis (bladder), urethritis (urethra), prostatitis (prostate gland), and epididymitis. Upper tract infections (such as pyelonephritis) involve the kidney and are referred to as pyelonephritis. Uncomplicated UTIs are not associated with structural or neurologic abnormalities that may interfere with the normal flow of urine or the voiding mechanism. Complicated UTIs are the result of a predisposing lesion of the urinary tract such as a congenital abnormality or distortion of the urinary tract, a stone, indwelling catheter, prostatic hypertrophy, obstruction, or neurologic deficit that interferes with the normal flow of urine and urinary tract defenses. 

Smooth or involuntary muscle is found within the wall of organs and structures such as the esophagus, stomach, intestines, bronchi, uterus, urethra, bladder and blood vessels. Unlike skeletal muscle, smooth muscle is not under conscious control. 

The lower urinary tract consists of the bladder, urethra, urinary or urethral sphincter, and the surrounding musculofascial structures including connective tissue, nerves, and blood vessels. The urinary bladder is a hollow organ composed of smooth muscle and connective tissue located deep in the bony pelvis in men and women. The urethra is a hollow tube that acts as a conduit for urine flow out of the bladder. The interior surface of both the bladder and urethra is lined by an epithelial cell layer termed transitional epithelium, which is in constant contact with urine. Previously considered inert and inactive, transitional epithelium may actually play an active role in the pathophysiology of many lower urinary tract disorders, including interstitial cystitis and UI. The urinary or urethral sphincter is a combination of smooth and striated muscle within and surrounding the most proximal portion of the urethra adjacent to the bladder in both men and women. This is a functional but not anatomic sphincter that includes a portion of the bladder neck or outlet as well as the proximal urethra. 

Simply stated, UI may occur only as a result of abnormalities of the urethra (including the bladder outlet and urinary sphincter) or the bladder, or from a combination of abnormalities of both structures. Abnormalities may result in either overfunction or underfunction of the bladder and/or urethra with the resulting development of UI. While this simple classification scheme excludes extremely rare causes of UI such as congenital ectopic ureters and urinary fistulas, it is useful in gaining a working understanding of the condition. 

DeLancey JO (1994) Structural support of the urethra as it relates to stress urinary incontinence The hammock hypothesis. Am J Obstet Gynecol 170 1713-1723... 

Fig. 12.1a-c. CT anatomy of the normal vagina. a,b CT. c Sagittal CT reconstruction. CT anatomy of the vagina - middle third at the level of the urinary bladder (a) and distal third at the level of the urethra (b). The vagina has the same density as the walls of the bladder, urethra, and rectum and can be distinguished from these structures on CT by the presence of a small fat layer. For differentiation of the vagina, it is also helpful if the bladder is filled with urine and the rectum is filled with air... 

Stones may form in all parts of the urinary excretory system, from the proximal tubules to the bladder and the urethra. Urinary stones are formed by the precipitation of organic or inorganic compounds normally in solution in the urine. Precipitation results from alterations of the urinary composition or the structure of the linings of the excretory canals. The gross appearance of stones is determined by their location in the urinary tract and by their chemical composition. 

Immediate treatment begins by placement of a tourniquet around the proximal shaft of the penis to avoid important hemorrhage. Then clots are removed, and the different structures are identified. Microsurgical approach is required for vascular and neural structures (Heymann et al. 1977 Carroll et al. 1985). The urethra is reapproximated, and end-to-end spatulated anastomosis is performed using a 4-0 Monocryl suture for the mucosa followed by a second layer suture of the spongiosa. 

The urethra is a tubular structure through which urine is expelled after accumulating in the physiological reservoir called the bladder. In men, this canal is also used by the seminal ducts and carries the sperm from the veru montanum all the way to the external urethral orifice. 

Fig. 19.1. Normal posterior urethra during rest in a young male. Endorectal end-fire probe in sagittal scan. The collapsed urethra is hypoechoic (arrowheads) with respect to the surrounding prostatic tissue, and a linear hyperechoic structure corresponds to the mucosa the hypoechoic outer line is due to the muscular layers...

The anterior urethra can be explored using high frequency linear probes that are able to examine the penile and perineal tract and the structures of the surrounding corpus spongiosum (Gluck et al. 1988 Nash et al. 1995). This exam consists of scanning performed after a saline solution is introduced... 

Fig. 19.3a,b. Sonourethrography. Normal appearance of the urethra in sagittal (a) and transversal (b) scans. The urethra distended hy the saline solution appears as an anechoic tubular structure well depicted with linear array transducer using direct skin contact on the ventral surface of the penis and with trans-scrotal and perineal scanning for bulbar urethra... 

Extremely rare in childhood, the urethral polyp is usually solitary and consists of a pedunculated structure, originating from the posterior urethra, developing in the bladder neck, which can prolapse in the urethra during micturition (Foster and Garrett 1986). Hematuria, nonneurogenic bladder-sphincter dysfunction and infection may reveal the abnormality. On ultrasound, it appears echo-genic. The main differential diagnosis of urethral polyp is an ectopic ureterocele that has ruptured either spontaneously (Fig. 6.8) or after endoscopic... 

Ectopic ureterocele develops at the lower end of the upper pole ureter of a duplicated kidney. It is a cyst-like thin-walled structure that is known to be mobile and variable in shape. During fetal life, the ureterocele can prolapse into the posterior urethra and create obstruction (Fig. 6.9). Bilateral hydronephrosis and megacystis can subsequently develop. Clinical diagnosis can be made at birth in girls with a perineal soft tissue mass, megacystis and bilateral urinary tract obstruction. Sonographic diagnosis can be difficult when the ectopic ureterocele has... 

Cobb s collar (Cobb et al. 1968) is a congenital narrowing of the bulbar urethra with no connection to the verumontanum (Dewan et al. 1994). It was shown that Cobb s collar is frequently associated with tubular or cystic dilatation of Cowper s glands ducts (also called syringocele) (Dewan 1996), both structures arising embryologically from the urogenital membrane area. 

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