Renal System: Upper and Lower Urinary Tract Functions

Upper Urinary Tract: Elimination

• Functions to eliminate urine from the kidney to the exterior
• Extends from calyces to urethra

Lower Urinary Tract: Excretion

• Extends from calyces to urethra
• Transits urine from kidney to exterior
• Bladder acts as a reservoir
• Lined by urothelium (transitional cell epithelium)
• Resists osmotic stresses of contact with urine

Disorders of the Lower Urinary Tract

• Infection
  • Often secondary to stasis
  • Usually due to gram-negative bacteria (E. coli) or gram-positive bacteria (Staphylococcus)
  • Commensals in the large bowel
  • Women are particularly prone
  • Diabetes mellitus also predisposes to infection
  • Symptoms:
    • Pain when urinating or burning sensation
    • Urinating small amounts frequently
    • Cloudy or foul-smelling urine
    • Blood in urine
  • Diagnosis:
    • Urine sample
    • Dipstick
    • Microscopic analysis
    • Culture (not routine, but useful to test antibiotic resistance)
  • Treatment:
    • Some can clear without treatment
    • Cranberry juice/sodium citrate sachets can relieve symptoms
    • Antibiotic treatment is usually fast and effective
    • Antimicrobial resistance varies in different areas of the country
    • Trimethoprim/Sulfamethoxazole for three days is good mini-dose therapy, but resistance rates are high in many areas
    • Nitrofurantoin is a good choice for uncomplicated UTIs, but it is bacteriostatic, not bactericidal, and must be used for 5-7 days
• Obstruction
  • Intrinsic (e.g., stone formation)
  • Extrinsic (e.g., tumor, pregnancy)
  • Obstruction of ureter:
    • Dilation of the ureter
    • Dilation of the renal pelvicalyceal system
    • Reabsorption of fluid by kidneys
  • Obstruction of urethra:
    • Bladder dilation
    • Hypertrophy of bladder wall
    • Predisposition to outpouching

Urinary Calculi

• Most commonly form in pelvicalyceal system and bladder
• Calculus is a "pebble" in Latin
• Solid aggregates of dietary minerals
• Calcium oxalate or phosphate are most common types of calculi
• Calculi are classified by their location
• Predisposing factors:
  • Increased solute concentration in the urine
  • Reduced solubility of solute in the urine
• Underlying causes:
  • Low fluid intake
  • Urine stasis
  • Persistent urinary tract infections
  • Primary metabolic disturbances

Types of Calculi

• Pelvicalyceal calculi:
  • Appearance depends on where calculi are formed
  • Calculi are often multiple and small (gravel-like)
  • Calculi in pelvicalyceal system predisposes to:
    • Infection
    • Squamous cell metaplasia
    • Carcinoma in metaplastic areas
• Staghorn calculi:
  • Most common, made up of struvite and calcium carbonate apatite
  • Caused by organisms that produce enzyme urease, which promotes the generation of ammonia and hydroxide from urea
• Ureter calculi:
  • Mostly develop in renal pelvis
  • Pass down urinary tract
  • Associated with loin pain
  • Treatment:
    • Small stones can pass naturally
    • Larger stones require surgical removal: shockwave lithotripsy, ureteroscopy, or percutaneous nephrolithotomy
• Bladder stones:
  • Spherical and laminated
  • Often large
  • Stasis and chronic infection
  • Can cause squamous metaplasia in urinary bladder