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
Main complications of lower urinary tract infection are acute & chronic
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
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
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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