Diseases of the Lower Urinary Tract

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The lower urinary tract extends from the calyces in the kidney to the distal end of the urethra, and is structurally adapted to transmit urine from the kidney to the exterior, the bladder being modified to act as a reservoir. The lower urinary tract is lined by urothelium (transitional-cell epithelium),} which is capable of resisting the osmotic stresses of contact with urine.

There are five main groups of disorders in the lower urinary tract: infection, which is often secondary to stasis of urine, following obstruction to flow; obstruction by intrinsic occlusion or extrinsic pressure; stone formation, which is often secondary to stasis of urine combined with infection; tumour formation, i.e. neoplasia of transitional-cell epithelium; and developmental abnormalities.

Shows spreading wave of infection, starting at the urethra, moving up into the bladder. Later infection can ascend into ureters, renal pelvis and calyces

Stone formation in calyces, pelvis, ureter or bladder

Tumour formation in pelvicalyceal system, ureter or bladder Causes of papillary necrosis
Main complications of lower urinary tract infection are acute & chronic pyelonephritis


Infections in the lower urinary tract are predisposed by obstruction and stasis

Lower urinary tract infection is usually due to 
Gram-negative coliform bacilli, e.g. E. coli and Proteus, which are normally commensals in the large bowel; because they have a short urethra, women are particularly prone to developing ascending infections. In men, lower urinary tract infection is usually associated with structural abnormalities of the lower urinary tract and stasis due to obstruction. Diabetes mellitus also predisposes to infection.

In most cases the lower urinary tract infection remains localized to the urethra and bladder, but organisms may ascend the ureter and enter the pelvicalyceal system, particularly when there is an obstructive lesion. An acute bacterial urethritis and cystitis may lead to an ascending ureteritis and pyelitis (inflammation of the renal pelvis and calyces). In this way, organisms may gain access to the renal parenchyma to produce acute pyelonephritis,} with the formation of abscesses in the renal medulla and cortex.

The pelvicalyceal system is dark reddish brown as a result of acute inflammation of the usually smooth creamy mucosal lining due to bacterial infection. The kidney is also congested and some small scattered abscesses are present in the cortex and medulla (acute pyelonephritis).

Causes of hydronephrosis

Obstruction of the drainage of urine from the kidney causes hydronephrosis

Obstruction, one of the most important consequences of disease of the lower urinary tract, may occur at any place in the tract:

Renal pelvis - calculi, tumours.

Pelviureteric junction - stricture, calculi, extrinsic compression.

Ureter - calculi, extrinsic compression (pregnancy, tumour, fibrosis).

Bladder - tumour, calculi.

Urethra - prostatic hyperplasia or carcinoma, urethral valves, urethral stricture.

If obstruction occurs in the urethra, the bladder develops dilatation and secondary hypertrophy of muscle in its wall. This predisposes to development of outpouching of the bladder mucosa (diverticulae).

If obstruction occurs in a ureter, there is dilatation of the ureter (megaureter),} with progressive dilatation of the renal pelvicalyceal system, termed hydronephrosis. Fluid entering the collecting ducts cannot empty into the renal pelvis and there is intrarenal resorption of fluid. At this stage, if the obstruction is relieved, renal function returns to normal. However, if obstruction persists, there is atrophy of renal tubules, glomerular hyalinization, and fibrosis. As an end-stage, the renal parenchyma becomes severely atrophic and renal function is permanently impaired.

Urinary tract obstruction also predisposes to infection and stone formation.
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