Pathology of the urinary system

vesicoureteral reflux

 (VUR): 

   - 

retrograde flow of urine up the ureters during micturition; may carry bacteria all the way up 

to the kidneys; 

   - 

a VUR is normally prevented by the oblique insertion of the ureter into the bladder wall, so 

that the ureter is compressed as the bladder contracts during micturition; this intravesical 

portion of the ureter thus acts as a functional vesicoureteral valve; 

   - 

some degree of VUR is common in puppies because of the short intravesical portion of their 

ureter; this reflux gradually decreases with age as this intravesical portion lengthens and 

assumes a more oblique angle through the bladder wall; 

   - 

normal ureteral peristalsis may be altered by cystitis, ureteritis, or even peritonitis, probably 

through loss of muscle tone of the bladder wall or ureteral wall; this predisposes to VUR; 

 

   ∙ 

urinary obstruction favors accumulation of bacteria because of relative urine stasis → favors 

development of pyelonephritis; 

 

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   ∙ 

the medulla is the part of the kidney most susceptible to infection: 

   - 

relatively hypoxic because of its relatively poor vascularity and the low hematocrit and long 

travel time of blood in its vessels; the relative hypoxia may depress the metabolism of 

leukocytes, and the poor vascularity may decrease the inflammatory response time; 

   - 

its hypertonic environment depresses the phagocytic activity of leukocytes; 

   - 

ammonia and other metabolic waste products or toxins concentrated in this part of the kidney 

may interfere with the inflammatory process, such as complement activation; 

 

   ∙ 

the most common bacteria isolated from cases of pyelonephritis are: 

 

   - 

cattle:  

Corynebacterium renale

 (specific urinary pathogen, and obligate parasite of urinary 

mucosae); 

 

   - 

pigs:  

Eubacterium suis 

(specific urinary pathogen; venereal transmission from carrier boars; 

during estrus in sows, estrogen causes the urine pH to rise, producing an alkaline 

environment suitable for the growth of this bacterium); 

 

   - 

dogs, cats: mostly members of the rectal flora (

E. coli

, 

Proteus

 species, 

Enterobacter

 species, 

Pseudomonas aeruginosa

); 

 

   ∙ 

the virulence of bacteria in the urinary tract is influenced by the expression of a wide variety of 

factors, such as surface fimbriae (which permit adherence to the urinary epithelium), non-fimbrial 

adhesins, hemolysin, anticomplementary serum resistance factor, etc..