Diseases of the Urinary System

Comprehensive practice vocabulary flashcards covering the anatomy, physiology, diagnostic tests, pathologies, and clinical catheterization techniques of the canine and feline urinary tract.

Kidneys

Paired urinary tract organs situated dorsally in the abdominal cavity that filter blood, remove nitrogenous wastes, and regulate fluid, electrolyte, and blood pressure homeostasis.

Ureters

Muscular ducts that transport urine from the renal pelvis of each kidney to the urinary bladder.

Urinary Bladder

A distensible muscular reservoir located in the caudal abdomen/pelvis that stores urine prior to micturition.

Urethra

The tubular passage through which urine is excreted from the urinary bladder to the outside of the body.

Primary Functions of the Urinary Tract

Four critical physiological roles: eliminating metabolic by-products, regulating water and electrolyte balance, regulating red blood cell ($\text{RBC}$) production, and regulating blood pressure.

Kidney Anatomical Location

Located in the dorsal part of the abdominal cavity, situated immediately ventral to the first through third lumbar vertebrae ($\text{L1--L3}$).

Equine Right Kidney

The right kidney of the horse, uniquely anatomical for having a heart-shaped appearance rather than a bean shape.

Bovine Kidneys

The kidneys of cattle, anatomically distinguished by having a distinctly lobulated external appearance.

Nephron

The microscopic structural and functional filtering unit of the kidney, comprising the renal corpuscle, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting tubule.

Renal Corpuscle

The initial filtration component of a nephron, consisting of the glomerulus surrounded by Bowman's capsule and its capsular space.

Glomerulus

A capillary network within the renal corpuscle that filters plasma, electrolytes, and metabolic wastes from blood into the proximal convoluted tubule.

Proximal Convoluted Tubule

The nephron segment receiving glomerular filtrate where the major reabsorption of essential solutes, water, and glucose back into circulation begins.

Loop of Henle

The U-shaped tubular segment of the nephron consisting of descending and ascending limbs that dips into the renal medulla to concentrate urine.

Distal Convoluted Tubule

The coiled nephron portion located between the ascending loop of Henle and the collecting tubule responsible for further selective secretion and reabsorption.

Collecting Tubule

The terminal tubular channel that gathers processed urine from multiple nephrons and serves as the primary target for antidiuretic hormone ($\text{ADH}$).

Glomerular Filtration Barrier

The specialized semipermeable filtration membrane of the glomerulus that allows fluid and small solutes to pass while preventing the entry of large proteins and blood cells unless damaged.

Tubular Resorption

The physiological recovery process in the renal tubules where filtered water, glucose, and essential electrolytes are transported back into systemic circulation.

Antidiuretic Hormone (ADH)

A pituitary hormone that acts on renal collecting ducts to promote water resorption and regulate total urine output volume.

Aldosterone

A mineralocorticoid hormone secreted by the adrenal cortex that regulates sodium, potassium, and fluid balance within the renal tubules.

Blood Urea Nitrogen (BUN)

A serum chemistry parameter measuring urea nitrogen to assess renal function; normally, approximately half ($50\%$) is reabsorbed in tubules and the remainder is excreted.

Urea

The principal nitrogenous end product of amino-acid breakdown in mammals, cleared by glomerular filtration.

Formation of urine

• Blood enters the renal corpuscle

• Plasma and wastes are filtered through the glomerulus into the next portion of the proximal convoluted tubule

  • Large proteins and cells do not enter unless damaged

• Filtered fluid passes through the rest of the nephrons

• Water and glucose are reabsorbed back into the body

Urine volume regulation

• The volume of urine produced is controlled by two hormones

  • antidiuretic hormone ( ADH)

    • released from the pituitary gland

    • acts on the collecting ducts to promote reabsorption of water

  • aldosterone

  • secreted by the adrenal cortex

The chemistry tests for kidney function

• Urea nitrogen ( blood urea nitrogen, aka BUN, also azostix)

• creatinine

• SDMA

• urinalysis

  • presence of proteinuria

  • urine specific gravity

• Other tests include various assays to evaluate the rate and efficiency of glomerular filtration

Azotemia

• Excessive amounts of urea and creatinine in the blood often indicate impaired kidney function.

• If BUN and creatinine are elevated on a chemistry panel, it indicates azotemia

Azostix

• A reagent test strip method referenced for rapid screening and evaluation of blood urea nitrogen ($\text{BUN}$) levels.

• reads azotemias

Blood urea nitrogen ( BUN)

• Urea is the principal end product of acid breakdown in mammals

• BUN is used to evaluate kidney function based on the kidney’s ability to remove the nitrogenous waste of urea from the blood

  • In normal conditions: all urea passes through the glomerulus and enters the renal tubules

  • Approximately half of the urea is reabsorbed; the remainder is excreted

  • If the kidney is not functioning properly, not enough urea is removed, leading to increased BUN levels

Causes of Elevated BUN

• Damaged kidneys not excreting waste

• Dehydration

  • increases retention of urea ( azotemia)

• High-protein diets

  • High levels of amino acids

• strenuous activity

  • Breakdown of amino acids

Creatinine

• A metabolic waste product of skeletal muscle breakdown that diffuses into the blood at a constant rate proportional to total muscle mass and is excreted by the kidneys.

  • Any condition that alters the glomerular filtration rate (GFR) will alter creatinine levels

  • used to evaluate renal function

  • not a sensitive indicator of kidney function

  • nearly 75% of kidney tissue must be nonfunctional before levels rise

Creatinine Diagnostic Sensitivity Threshold

An insensitive early indicator of renal disease because nearly $75\%$ of functional kidney tissue must be nonfunctional before serum creatinine levels rise above normal.

Glomerular Filtration Rate (GFR)

The volume of fluid filtered through glomerular capillaries per unit time; any condition that alters GFR directly alters serum creatinine concentration.

Symmetric Dimethylarginine (SDMA)

An innovative renal-function-specific biomarker that is more reliable than creatinine for detecting acute and chronic renal disease.

Clinical Significance of SDMA

Enables earlier diagnosis of both acute and chronic kidney disease and supports earlier and more effective veterinary treatment planning.

Urinalysis (UA)

A standard laboratory evaluation of urine assessing physical parameters, chemical constituents (such as proteinuria), specific gravity, and sediment.

Proteinuria

The abnormal presence of detectable protein in the urine, indicating potential glomerular barrier damage or tract inflammation.

Urine Specific Gravity (USG)

A refractometric measurement comparing urine density to water, reflecting the renal tubules' concentrating and diluting ability.

Azotemia

The clinical condition characterized by excessive amounts of nitrogenous waste products—specifically elevated blood urea nitrogen ($\text{BUN}$) and creatinine—in the blood.

Oliguria

Decreased production of urine by the kidneys.

Polyuria

Increased production of urine by the kidneys.

Pollakiuria

The frequent voiding of abnormally small amounts of urine.

Stranguria

Straining, difficulty, or discomfort associated with the act of urinating.

Dysuria

Painful or difficult urination.

Anuria

The complete absence of urine production.

Pyuria

The presence of pus or excessive white blood cells ($\text{WBCs}$) in the urine, signifying inflammation or infection.

Hematuria

The presence of blood or intact erythrocytes in the voided urine.

Tenesmus

Difficult, painful, or straining defecation; commonly seen in male dogs with prostate enlargement compressing the rectum.

Bacterial Cystitis

• Inflammation and/or infection of the urinary bladder

• Clinical signs: polyuria, pollakiuria, hematuria, stranguria, pyuria, dysuria, inappropriate urination, excessive licking of the urogenital area, and pain on caudal abdominal palpation.

Canine Cystitis

The most common cause of urinary tract disease in dogs, predominantly resulting from ascending bacterial urinary tract infection.

Symptoms: increased frequency of urination, cloudy urine, abnormal odor, hematuria, and dysuria. Frequent licking of the urethral area

Bacterial Pathogens in Canine Cystitis

Bacterial species identified on urine culture including Escherichia coli, Streptococcus, Staphylococcus, Proteus, Klebsiella, and Pseudomonas.

How to diagnose and treat canine cystitis

• Diagnosis: UA, urine culture to look for bacteria

• Treatment: antibiotics based on culture and sensitivity

  • Acute treatment for 10-14 days; chronic treatment for 4-6 weeks

Feline Bacterial Cystitis

Bacterial infection of the feline bladder that is much less common than in dogs and presents with signs resembling non-bacterial lower tract disease.

Abnormal Feline Urine Sediment WBC Threshold

The finding of greater than $5\text{--}8\,\text{WBCs/HPF}$ (white blood cells per high-power field) in feline urine sediment, which is considered abnormal.

Feline Lower Urinary Tract Disease (FLUTD)

An umbrella term for non-specific conditions of the feline bladder and urethra, also called feline cystitis, Feline Urological Syndrome ($\text{FUS}$), or Feline Idiopathic Cystitis ($\text{FIC}$).

Signalment and Risk Factors for FLUTD

Predisposing factors including middle age, obesity, indoor housing, exclusive dry-food diets, multi-cat households, boredom, and environmental stress.

Environmental Triggers of FLUTD

Routine disruptions such as owner absence, diet changes, litter brand modifications, moving litter box locations, or uncleaned litter boxes.

Natural Disease Course of FLUTD

A frequently recurrent, non-curable disorder where individual non-obstructed episodes are often self-limiting and resolve within $7\text{--}10\,\text{days}$.

Environmental Enrichment for FLUTD

Stress-reduction measures including scratching posts, toys, hiding places, exercise, outdoor leash walks, and synthetic pheromone diffusers or sprays.

Litter Box Management in FLUTD

Husbandry practices that involve providing an increased number of litter boxes in the household and completely changing the litter every $24\,\text{hours}$.

Therapeutic Diets for FLUTD

Formulated prescription diets designed to manage urinary tract health and urine composition, including Royal Canin SO, Hill’s c/d, and Iams Urinary Care.

Supportive Medical Therapies for FLUTD

Therapies including increased water intake, subcutaneous ($\text{SQ}$) fluids, cautious anti-inflammatories, analgesics, Cosequin nutraceuticals, and behavioral medications.

Predisposing Factors for Recurrent UTIs

Bacterial resistance, inappropriate antibiotic therapy, diabetes mellitus, immunosuppression, renal disease, hyperadrenocorticism, and urinary calculi.

Uroliths (Urolithiasis)

Multicrystalline mineral and mucoprotein concretions (bladder stones); urolithiasis refers to their formation within supersaturated urine anywhere in the urinary tract.

Radiopaque vs. Radiolucent Uroliths

Urinary calculi visible on survey radiographs due to high mineral density (radiopaque, e.g., struvite, calcium oxalate) versus those requiring contrast radiography to visualize (radiolucent, e.g., urates).

Struvite Crystals

Magnesium ammonium phosphate crystals classically forming in alkaline urine that display a distinctive coffin-lid rectangular prism microscopic appearance.

Calcium Oxalate Crystals

Urinary crystals forming in neutral to acidic urine, commonly presenting under microscopy as square, octahedral envelope shapes.

Ammonium Urate Crystals

Purine-derived crystals visible under light microscopy as brown, spherical structures with irregular spicules, termed thorn-apple crystals.

Breeds Predisposed to Canine Urolithiasis

Small companion breeds exhibiting high genetic or metabolic susceptibility to developing bladder stones, including the Bichon Frise, Shih Tzu, and Maltese.

Canine Urolithiasis Management Options

Therapeutic strategies including medical dietary dissolution, antimicrobial therapy based on culture, or surgical cystotomy removal.

Hill's s/d Diet

A calculolytic therapeutic diet designed to alter urine pH and dissolve struvite uroliths over a $4\text{--}8\,\text{week}$ course.

Maintenance Diets for Urolithiasis

Long-term nutritional formulas used following stone dissolution or surgery to prevent recurrence, including Hill’s c/d Multicare, Royal Canin SO, and Purina UR.

Radiographic Monitoring for Urolith Dissolution

Serial radiographic examinations performed every $2\text{--}4\,\text{weeks}$ to confirm progressive reduction in stone size during medical dissolution.

Cystotomy

Surgical incision into the urinary bladder to manually remove uroliths or obtain tissue biopsies.

Pyelonephritis

Bacterial infection and inflammation of the renal pelvis and kidney, typically ascending from a lower urinary tract infection.

Clinical Signs of Pyelonephritis

Systemic and localized signs comprising fever, flank pain, vomiting, lethargy, and polyuria/polydipsia ($\text{PU/PD}$).

Hematologic Findings in Pyelonephritis

Diagnostic bloodwork abnormalities revealing leukocytosis, elevated kidney chemistry values ($\text{BUN}$ and creatinine), and non-regenerative anemia.

Treatment Protocol for Pyelonephritis

High-dose targeted antibiotic administration for an extended period of $6\text{--}8\,\text{weeks}$, accompanied by fluid therapy to protect kidney function.

Post-Treatment Reculture for Pyelonephritis

Mandatory follow-up urine culture performed exactly $2\,\text{weeks}$ after completing antibiotics to confirm complete infection eradication.

Feline Urethral Plugs

Obstructive casts composed of small variable amounts of crystalline minerals embedded in a rich organic matrix of mucoproteins.

Anatomical Predisposition to Urethral Obstruction in Male Cats

A mechanical vulnerability in male cats caused by their longer, narrower, and less distensible penile urethra.

Clinical Signs of Feline Urethral Obstruction

Straining to urinate with little or no urine, repeated litter box visits, vocalizing, hematuria, anuria, perineal licking, anorexia, vomiting, and collapse.

Owner Misinterpretation of Feline Urinary Straining

A common clinical misconception where clients mistake a male cat straining in the litter box for constipation or difficulty defecating.

Physical Examination Findings in Feline Urethral Obstruction

Gentle caudal abdominal palpation revealing a markedly distended, painful, firm, and hard urinary bladder.

Biochemical Abnormalities in Urethral Obstruction

Severe post-renal elevations in blood urea nitrogen ($\text{BUN}$), creatinine, and phosphorus.

Life-Threatening Sequelae of Untreated Urethral Obstruction

Rapid development of severe electrolyte derangements, post-renal acute kidney failure, urinary bladder rupture, and death.

Medical Desobstruction of Feline Urethral Plugs

Emergency placement of a urinary catheter with retrograde sterile saline flushing to dislodge the plug, followed by intravenous fluids, analgesics, and anti-inflammatories.

Perineal Urethrostomy (PU)

A surgical salvage procedure creating a permanent, wider urethral opening in male cats with recurrent obstructions or unresolvable urethral stones.

Acute Renal Failure (ARF)

An abrupt decline in glomerular filtration following nephron damage, causing rapid accumulation of uremic acids and nitrogenous wastes in the blood.

Clinical Signs of Acute Renal Failure

Acute oliguria or polyuria, polydipsia, fever, painful kidneys on palpation, vomiting, diarrhea, anorexia, and dehydration.

Nephrotoxic Drugs Causing ARF

Therapeutic medications capable of causing acute tubular injury, including aminoglycoside antibiotics, sulfonamides, and chemotherapy drugs.

Lily Toxicity in Cats

Ingestion of plants from the Lilium and Hemerocallis families (daylilies) that causes severe acute renal failure and tubular necrosis in cats.

Management and Prognosis of Acute Renal Failure

Treatment with IV fluids, intestinal protectants, anti-nausea medication, and nutritional support; prognosis is guarded and kidney function may not fully normalize.

Chronic Renal Failure (CRF)

An irreversible, progressive loss of functional renal mass over months to years, occurring more commonly in older cats than dogs.

Clinical Signs of Chronic Renal Failure

Lethargy, weight loss, anorexia, polyuria/polydipsia, stomatitis, oral uremic ulcers, non-regenerative anemia, vomiting, feline gait disturbances, and sudden blindness.

Dietary and Medical Management of Chronic Renal Failure

Supportive care with IV or subcutaneous fluids, blood pressure control, appetite stimulants, and low-protein diets such as Hill’s k/d, Renal LP, or Purina NF.

Canine Urinary Incontinence

Loss of voluntary control of urination common in older spayed females (post-spay), characterized by passive urine leakage while asleep or exercising.

Phenylpropanolamine (Proin)

A sympathomimetic oral medication ($\text{PPA}$) used to medically treat urinary sphincter incontinence in dogs by increasing internal urethral sphincter tone.

Diethylstilbestrol (DES)

A synthetic estrogen compound utilized to treat hormone-responsive post-spay urinary incontinence in female dogs.

Canine Prostatic Disease

Prostate enlargement under chronic hormonal stimulation in intact male dogs, causing tenesmus, stranguria, hematuria, and dysuria; treated by neutering, antibiotics, or size-reducing drugs.

Transitional Cell Carcinoma (TCC)

The most common malignant neoplasm of the canine and feline urinary bladder, typically visualized as an irregular intravesical mass on ultrasound.

Cystocentesis Contraindication in Bladder Tumors

Peritoneal needle aspiration of the bladder is contraindicated when transitional cell carcinoma is suspected due to the risk of iatrogenic tumor cell seeding into the abdominal cavity.