Lecture 36: Ureters, Urinary Bladder, and Urethra

what is the tubular continuation of the renal pelvis that enters the urinary bladder wall obliquely?

ureters

the ureters are covered by

a mucosal flap called the vesicoureteral valve

what does the vesicoureteral valve do?

prevents reflux of urine from the bladder back into the ureter

what lines the ureters?

pseudostratified transitional epithelium that is normally smooth and glistening

what is the function of the ureters?

propel urine from renal pelvis to bladder via peristalsis

urinary bladder

• expansile, muscular sac

• normal mucosa is smooth and glistening

• urine should be translucent

why is urine cloudy in horses?

the abundant excretion of calcium in the form of calcium carbonate crystals and mucus produced in renal pelvis and proximal ureter

what is the function of the urinary bladder?

store and expel urine

what is continence in the urinary bladder?

detrusor muscle relaxed and leakage prevented by activated urethral sphincter and contraction of urethral muscles

what is micturition?

contracted detrusor muscle moves urine through relaxed urethra

what is the tubular continuation of the urinary bladder that directs urine out of the body?

urethra

why are females predisposed to ascending UTIs?

they have a relatively short urethra

why do males have higher risk of lower urinary tract obstructions?

their urethra travels a more elongated course

in all male animals, the urethra courses over the ischial arch, which may result in

narrowing of the luminal diameter and potentially allows obstructions to form

where is a common location for obstructions in ruminants/pigs?

sigmoid flexure

where is an area of obstruction in dogs?

os penis

what is a common location of obstruction in small ruminants?

the narrow urethral process extending from the tip of the glans penis

what is the most common source of disease in the urinary system?

• obstruction of flow → pressure necrosis

• infectious causes leading to inflammation

• accumulation of toxic metabolites can result in infection, hyperplasia, metaplasia, or neoplastic transformation

ascending infection of urinary system

• contamination for GI, skin or repro tract

• blind ended tubular system with one exit → predispose to bacterial ascension

• more adherent bacteria may ascend to renal pelvis via vesicoureteral reflux

• urine stasis and infrequent urination can predispose to disease

descending infection of urinary system

from kidney/renal pelvis

how is exposure from lumen considered a portal of entry?

toxin accumulation or trauma from urolith

what are defense mechanisms of the urinary system?

• flushing action of urine minimizes risk for bacterial adherence

• peristalsis that eliminates bacteria

• inhospitable environment for bacterial growth controlled by urine pH and osmolarity

• protective urothelial mucus coating

• innate and humoral immune response

where should an ectopic ureter terminate?

in trigone on urinary bladder

true or false: ectopic ureters are more predisposed to obstruction or infection.

true

ectopic ureters may present with

incontinence or urine dribbling

predisposed breeds to ectopic ureters

labs, huskies, westies, fox terrier, mini and toy poodles

patent urachus is most commonly seen in

foals

what is the urachus?

tube in umbilical cord that drains urine from fetal bladder to allantoic sac in placenta

what happens if the urachus fails to close?

can dribble urine from umbilicus, susceptible to ascending infection

the urachus is the direct channel between

urinary bladder and umbilicus

true or false: patent urachus is the most common malformation of urinary bladder.

true

hydroureter

• dilation of the ureters

• most often caused by obstruction of urine outflow because of blockage of the ureters by calculi, chronic inflammation, lumina or intramural neoplasia, or accidental partial ligation

what is this arrow pointing to?

calculus in ureter lumen

what is urolithiasis?

presence of stones or calculi (uroliths) in the urinary collecting system

when do uroliths form?

when genetic, dietary, and pathophysiologic factors occur together and cause the precipitation of excretory metabolites in urine into grossly visible stones

uroliths are least common in the

renal pelvis

urinary pH

• oxalates precipitate at acid pH

• struvites and carbonates precipitate at alkaline pH

what are urinary calculi?

aggregations of precipitated mineral admixed with urinary proteins and proteinaceous debris

silica calculi

have a unique, pronged appearance that resembles jacks

large renal pelvic calculi classically have a

staghorn appearance

what are urinary calculi composed of?

fine, sandlike material, which causes cloudy urine

what type of calculi is this?

silica calculi (jacks)

what type of calculi is this?

staghorn

what type of calculi is this?

smooth struvite

what type of calculi is this?

ammonium biurate calculi

what type of calculi is this?

calculi in penile urethra of cat

male cats with urinary obstruction

urethral plugs → fine struvite (sand) with rubbery protein matrix can occlude urethra leading to obstruction

female cats with urinary obstruction

more often calculi leading to obstruction in urinary bladder or renal pelvis

what is the most common kind of crystal in dogs historically?

struvite → possibly diet related

what is the more common calculi in dogs?

calcium oxalate → can be seen with cushings, hyperparathyroidism, hypercalcemia or exogenous steroids

what calculi is more common in dalmations because they excrete high concentrations of uric acid?

urate stones

urate stones are an autosomal recessive trait resulting in

incomplete conversion of uric acid to allantoin

urolithiasis in ruminants

• silica and struvite can cause obstructions most often in bulls and steers at the sigmoid flexure

• severe cases - rupture from accumulation of urine

acute cystitis

• bacterial infection is the most common cause

• E. coli is the most common implicated bacteria across species

• more common in females

why is the bladder resistant to infection?

because of the flushing action of normal urine flow that quickly removes contaminating material

factors that promote bacterial colonization in urinary bladder

• bacteria

• host → decreased urination, urine retention, immune suppression

• disruption of urothelium

• bacteria growth enhanced if glucosuria

what are the 3 different forms of chronic cystitis

diffuse, follicular, polypoid

diffuse chronic cystitis

mucosa reddened and thickened

follicular chronic cystitis

• nodules white-gray nodular proliferations bordered by hyperemia (cobblestone appearance)

• most common in dogs

• most common with accompanying urolithiasis

polypoid pattern of chronic cystitis

polyps arising in the bladder mucosa are composed of a core proliferative connective tissue covered by surface epithelium and mononuclear inflammation

polypod pattern of chronic cystitis is what kind of response?

inflammatory/hyperplastic

mycotic cystitis

• candida albicans

• aspergillus sp.

• secondary to chronic bacterial cystitis/immune suppression

• prolonged antimicrobial therapy

feline idiopathic cystitis

• common cause of feline lower urinary tract disease

• more common in middle aged, overweight, male indoor cats

• lesions nonspecific

canine cystitis

cyclophophamide induced hemorrhagic cystitis

cantharidin hemorrhagic cystitis

• horses

• ingestion of blister beetles from hay or contaminated products

• beetles contain cantharidin

• hemorrhagic erosive cystitis

• GI ulceration and colitis

bracken fern cystitis

• hematuria that can be associated with neoplasia

• chronic ingestion of bracken fern

• all parts of fern are toxic

what is the principle carcinogen within bracken fern?

ptaquiloside

neoplasia

• most common in bladder

• most common in dogs, occasionally in cats, rare in other species

• scottish terriers, shetland sheepdogs, beagles and collies increased risk

what % of tumors are epithelial tumors?

80%

papillomas

• multiple and may have a pedunculated or sessile appearance

• composed of well-differentiated urotehlium

urothelial cell carcinomas

• focal, raised nodules or diffuse thickenings of the urinary bladder wall

• most common in the trigone region of the bladder

in cats, urothelial cell carcinomas tend to arise

at sites in the bladder distant from the trigone

squamous cell carcinomas and adenocarcinomas

• small portion of bladder neoplasms

• less likely to metastasize than urothelial carcinomas

what is this picture showing?

urothelial carcinoma in dog → multilobulated mass protruding into lumen

mesenchymal tumors

• fewer than 20% of neoplasms

• leiomyoma

• fibroma

• rhabdomyosarcoma

• lymphosarcoma

• hemangiosarcoma

what is one of the best models of toxic induced neoplasia in vet med?

bracken fern neoplasia

cattle chronically ingesting bracken fern can have incidence of neoplasia up to

25%

where is bracken fern neoplasia most commonly located?

on ventral and lateral bladder wall due to more frequent contact with toxic metabolites in the urine