Diseases of the lower urinary tract
Consequences of urolithiasis
Some general things to remember before we start this unit:
1. The lower urinary tract consists of ureter, urinary bladder, and urethra
2. The renal pelvis, ureters, and urinary bladder are lined by transitional epithelium. The horse bladder has islands of stratified squamous epithelium scattered among the transitional epithelium. The distal urethra is lined by stratified squamous epithelium. The lamina propria has small lymphoid follicles that may be large enough to be seen grossly (2-4 mm discrete, white foci).
3. The vesicoureteral valve (formed by the oblique passage of the ureter through the bladder wall) normally prevents reflux of bladder urine into the ureter and renal pelvis.
4. The urinary bladder often constricts at death and may appear very thick walled.
5. The urine is normally clear except in a few species such as the horse where it is cloudy due to mucus and fine crystals.
Ureteral aplasia is rare but may be seen with renal aplasia
Ectopic ureters. Normally the ureters enter the trigone of the bladder. When they enter elsewhere they are termed ectopic. Ectopic ureters are mostly found in dogs and then certain breeds are at higher risk (e.g. Siberian husky dogs). They are a common cause of urinary incontinence in young female dogs.
Patent urachus is probably the most common bladder malformation. This develops when the urachus fails to close thus forming a direct channel between the bladders apex and the umbilicus. Foals seem to be affected most frequently and will be seen dribbling urine at the umbilicus.
Failure of urachal involution and sometimes patency may be seen in association with neonatal omphalitis.
Bladder diverticula are outpocketings of the bladder wall that may be acquired or congenital.
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