Renal/Urologic System: Key Concepts (Ch.57-60)

Anatomy and Function of the Kidneys

• Location: retroperitoneal, behind peritoneum; one kidney on each side of the spine.

• Size: $4{-}5\text{ inches} \approx 10{-}13\text{ cm}$ long; $2{-}3\text{ inches} \approx 5{-}7\text{ cm}$ wide; about $1\text{ inch} \approx 2.5{-}3\text{ cm}$ thick.

• Laterality: left kidney slightly longer and narrower than the right.

• Blood supply: kidney blood flow $600{-}1300\ \text{mL/min}$.

• Functional unit: nephron; $\approx 1{,}000{,}000$ nephrons per kidney.

• Major hormones/products: renin (RAAS regulation), erythropoietin, activated vitamin D.

Urine Formation: Filtration, Reabsorption, Secretion

• Juxtaglomerular complex: specialized cells in afferent/efferent arteriole and distal tubule; produce renin to regulate blood flow, GFR, and BP.

• Filtration (glomerular): water, electrolytes, creatinine, urea nitrogen, glucose cross glomerular membrane into Bowman's capsule, forming glomerular filtrate.

• Proximal tubule: filtrate becomes tubular filtrate (early urine).

• GFR: filtration rate expressed in mL/min; normal GFR \approx $125\ \text{mL/min}$, about $180\ \text{L/day}$ filtrate.

• Reabsorption: tubular reabsorption returns most filtrate to blood; normal urine output $1{-}3\ \text{L/day}$.

• Secretion: substances move from blood into urine (e.g., K(^{+}), H(^{+})) to maintain fluid/electrolyte and acid-base balance.

• Regulation: GFR is autoregulated by constriction/dilation of afferent and efferent arterioles; drops in systolic BP (below ~$65{-}70\ \text{mmHg}$) impair GFR maintenance.

Glomerular Filtration Rate (GFR) and Thresholds

• Glomerular filtration rate (GFR) control by blood pressure/flow; kidneys self-regulate to keep GFR constant.

• Renal threshold for glucose reabsorption: >180\ \text{mg/dL}; below threshold, glucose reabsorbed; above threshold, glucose appears in urine.

• Importance: GFR and tubular function determine waste elimination and urine concentration.

Hormones and Kidney Products

• Renin: part of juxtaglomerular complex; regulates blood flow, GFR, and BP via RAAS.

• Other products: prostaglandins, erythropoietin, activated vitamin D; kinins influence kidney blood flow and perfusion.

Ureters and Bladder; Urethra Basics

• Ureter: single per kidney, hollow tube connecting renal pelvis to bladder; diameter $\approx \tfrac{1}{2}\text{ inch}$ (1.25 cm); length $12{-}18\text{ inches}$ (30–45 cm).

• Bladder: muscular sac, stores urine, enables continence and voiding; urothelium secretions resist bacteria.

• Urethra: conduit for urine elimination.

• Male urethra length: $6{-}8\ inches$ (15–20 cm); Female: $1{-}1.5\ inches$ (2.5–3.75 cm).

Urinary Continence and Voiding

• Continence: maintained by detrusor relaxation, internal sphincter tone, external sphincter contraction; coordinated control.

• Voiding reflex: detrusor contraction with relaxation of external sphincter and pelvic floor; learned voluntary control via cerebral cortex and brainstem.

Age-Related Changes

• Kidneys: cortical tissue loss with age; nephron loss ~decade-wise; medulla preserved.

• GFR and concentration: reduced ability to concentrate urine; increased urgency/nocturnal polyuria.

• Bladder: detrusor elasticity decreases; pelvic floor weakness more common in women; enlarged prostate in men affecting voiding.

• Hemodynamics: blood flow to kidney declines ~10% per decade; increased vulnerability to hypotension/hypertension.

General Assessment & History (Urinary Focus)

• Nonmodifiable risk factors: age, sex, race/ethnicity; sudden hypertension in >50 suggests kidney disease; cystic kidney disease often presents in 40s–50s.

• Socioeconomic and access issues affect prevention, detection, and adherence.

• Pregnancy history (proteinuria, HTN, gestational DM) important.

Diagnostic Assessment: Labs

• Serum creatinine: produced from muscle; baseline varies with muscle mass; doubling of serum creatinine ~ 50% reduction in GFR.

• BUN: measures kidney excretion of urea nitrogen; ratio BUN/creatinine helps differentiate dehydration/low perfusion vs intrinsic kidney disease.

• Cystatin-C: alternative GFR indicator, not influenced by muscle mass; may predict CKD progression.

• Urine tests:

  • Specific gravity: $1.005{-}1.030$; Osmolarity: variable; typical urine osmolarity 300–900 mOsm/kg under normal hydration.

  • pH: normal urine pH $4.6{-}8;\text{average }6$.

  • Protein: normally none; proteinuria may indicate glomerular/renal disease; albumin-to-creatinine ratio (ACR) stages: A1 none-to-micro (<$30\ \text{mg/g creatinine}$), A2 30–300, A3 >300.

  • Glucose: glucose in urine when renal threshold exceeded (>$180\ \text{mg/dL}$).

  • Ketones: normally none.

  • Leukocyte esterase: positive indicates WBCs/inflammation; nitrites indicate bacterial infection.

  • RBCs/WBCs, casts, crystals: indicate infection, inflammation, or stone disease.

• Creatinine clearance: approximation of GFR; normal ranges: $107{-}139\ \text{mL/min}$ (men), $87{-}107\ \text{mL/min}$ (women) using 24-hr urine; age-related decline with time.

• BUN:Cr ratio: helps distinguish pre-renal vs renal causes; high ratio suggests dehydration/low perfusion; both rising suggests renal dysfunction.

Diagnostic Assessment: Imaging and Procedures

• Bladder scanners: screen postvoid residuals to guide catheterization decisions.

• KUB X-ray: gross anatomy and stones; CT with/without contrast: detailed anatomy; contrast risk in CKD; MRI: improved soft-tissue contrast; ultrasound: no radiation, assesses kidney size, perfusion via Doppler, obstruction.

• Radiologic contrast risks: iodinated contrast can injure kidneys; gadolinium: nephrogenic systemic fibrosis risk.

• Cystoscopy/Cystourethroscopy: direct visualization of bladder/urethra; may diagnose or treat lesions; often under anesthesia.

• Urodynamics: assess bladder capacity, pressure, flow, and pelvic floor muscle function for incontinence.

• Urine cultures: used for suspected infection; clean-catch preferred; catheterization if needed.

Urinary Incontinence: Types and Management

• Types: stress, urge (OAB), overflow, functional, mixed.

• Stress: leakage with increased abdominal pressure; pelvic floor weakness; treat with pelvic floor training, surgical slings, bulking agents.

• Urge: sudden urge with leakage; treat with antimuscarinics (e.g., oxybutynin, tolterodine), sometimes Botox detrusor injections.

• Overflow: incomplete emptying; manage with bladder compression techniques (Credé, Valsalva), double-voiding, and intermittent catheterization.

• Functional: due to cognitive/physical impairment; interventions focus on containment and routine.

• Nonpharmacologic: bladder training, scheduled voiding, pelvic floor exercises (Kegels), biofeedback, vaginal cones, pessaries, external collection devices (condom catheter, PureWick).

• Nursing considerations: assess skin integrity to prevent incontinence-associated dermatitis (IAD); provide education, support, and device management.

Urinary Tract Infections, Cystitis, and Urothelial Cancer

• Cystitis: bladder inflammation; can be infectious (UTI) or noninfectious (irritants, radiation).

• Common UTI pathogens: Escherichia coli; Candida; complicated UTIs require broader testing and longer antibiotics.

• Catheter-associated risk increases with duration of catheterization; manage with aseptic technique and timely removal.

• Urothelial (bladder) cancer: often presents with painless hematuria; smoking is a major risk factor; diagnosis via cystoscopy and biopsy; intravesical therapy (BCG) used post-diagnosis.

Urolithiasis (Kidney Stones)

• Stones form from supersaturation of urine with stone-forming elements (calcium, uric acid, struvite, cystine).

• Most stones are calcium-based; dehydration is a key risk factor.

• Pain: renal colic with flank pain; severe, sudden, may radiate to groin.

• Diagnosis: noncontrast CT abdomen/pelvis is gold standard; ultrasound in pregnancy; KUB X-ray optional.

• Management: analgesia (opioids/NSAIDs with caution), anti-spasmodics; medical expulsive therapy with tamsulosin for stones 5–10 mm; hydration; consider SWL (shock wave lithotripsy), ureteroscopy with stone removal, or percutaneous procedures depending on size and location.

• Prevention: high fluid intake; dietary adjustments; urine alkalinization for specific stone types; pharmacologic prevention (e.g., thiazide diuretics for hypercalciuria, allopurinol for uric acid stones, potassium citrate for uric acid/stone prevention).

Polycystic Kidney Disease (PKD)

• Genetics: usually autosomal dominant; liver cysts common; cerebral aneurysm risk higher.

• Hypertension common; pain, infection, and cyst complications frequent.

• Imaging: ultrasound first-line for diagnosis; MRI/CT for detailed assessment.

• Management focuses on BP control, pain management, and delaying progression; dialysis or transplantation as CKD progresses.

Chronic Kidney Disease (CKD) Overview and Stages

• CKD: progressive, irreversible disorder lasting >3 months; can progress to end-stage kidney disease (ESKD).

• GFR-based staging:

  • Stage 1: GFR > 90 with kidney damage

  • Stage 2: GFR 60–89

  • Stage 3: GFR 30–59 (3a: >45, 3b: 30–44)

  • Stage 4: GFR 15–29

  • Stage 5: GFR <15 or dialysis dependence

• Albuminuria stages (A1-A3): A1 none-to-micro (<$30\ \text{mg/g creatinine}$), A2 30–300, A3 >300.

• Common CKD complications: anemia, electrolyte imbalances (K+, Ca/P), metabolic acidosis, bone disease (renal osteodystrophy), hypertension, fluid overload, malnutrition, cardiovascular disease; uremia with systemic effects.

• Management goals: slow progression, manage complications, early dialysis/transplant planning.

End-Stage Kidney Disease (ESKD) and Kidney Replacement Therapy (KRT)

• KRT options: hemodialysis (HD), peritoneal dialysis (PD), kidney transplantation.

• Hemodialysis (HD): life-sustaining; typically 3×4-hour sessions/week; central access via AV fistula/graft; monitor for hypotension, electrolyte shifts, and bleeding.

• Peritoneal dialysis (PD): CAPD or APD/IPD; uses peritoneal membrane; risks include peritonitis and exit-site infection; protein loss and membrane function considerations.

• Kidney transplantation: life-extending, not a cure; donor types include living related, NHBD, cadaveric; immunologic matching (HLA, ABO); lifelong immunosuppression required; rejection and infection risks.

• Vascular access for HD: AV fistula (preferred) or AV graft; maturation can take weeks to months; monitor for bruit, thrill, and distal pulses; catheter-based temporary access as needed.

• PD catheter care and exit-site management; monitor for infection and dialysate flow issues.

Nutrition, Medication, and Drug Considerations in CKD

• Protein: CKD nutrition often requires protein restriction depending on stage; dialysis patients require higher protein intake (roughly $1.0{-}1.3\ g/kg/day$ or $1.2{-}1.5\ g/kg/day$ for PD per guidelines).

• Sodium: restrict to manage fluid balance; 1–3 g/day common in non-dialysis CKD; higher allowances with dialysis depending on intake/output.

• Potassium: restrict in CKD with reduced excretion; limit to $60{-}70\ mEq/day$ or adjust per individual needs.

• Phosphorus: restrict; phosphate binders may be used with meals; monitor calcium and vitamin D; avoid aluminum-containing binders long-term.

• Fluids: restrict in CKD depending on urine output and volume status; aim for balanced hydration without overload.

• Vitamins: water-soluble vitamins may be required due to dialysis losses; dietary counseling essential.

• Drugs: many antibiotics, diuretics, anticoagulants require dose adjustments in CKD; monitor for nephrotoxicity; avoid NSAIDs when possible due to renal autoregulation impairment.

• Dialysis considerations: during HD, avoid nephrotoxic or high-risk meds; consider dialysis timing when giving certain drugs (e.g., antibiotics) to maintain efficacy.

Special Topics: Imaging, Procedures, and Safety

• Contrast media: iodinated contrast risks; gadolinium risks (nephrogenic systemic fibrosis); assess kidney function before imaging.

• Urinalysis interpretation: look for protein, glucose, ketones, leukocyte esterase, nitrites, RBCs, WBCs, casts, crystals; normal coagulations and bichemistry guides treatment.

• 24-hour urine collection: used for precise testing including creatinine clearance; important for CKD staging and drug dosing.

Key Numbers to Recall (Quick Reference)

• GFR normal: \approx $125\ \text{mL/min}$; daily filtrate \approx $180\ \text{L/day}$; typical urine output $1{-}3\ \text{L/day}$.

• Glucose renal threshold: >180\ \text{mg/dL}.

• Normal kidney size (adult): $4{-}5\ \text{inches}$ long; $2{-}3\text{ inches}$ wide.

• Nephrons: \approx $1{,}000{,}000$ per kidney.

• Ureter length: 12{-}18\"; diameter \approx 1/2\".

• Normal specific gravity: $1.005{-}1.030$.

• Urine pH: $4.6{-}8$ (avg ~6).

• Albumin-to-creatinine ratio (CKD stages): A1 < $30\ \text{mg/g}$; A2 30–300; A3 > $300\ \text{mg/g}$ .

• CKD stages (GFR): Stage 1 > $90\ mL/min/1.73\,m^2$; Stage 2 $60{-}89$; Stage 3 $30{-}59$; Stage 4 $15{-}29$; Stage 5 < $15$.

• Creatinine clearance (normal): men $107{-}139\ \text{mL/min}$; women $87{-}107\ \text{mL/min}$ (24 h collection).

• CKD nutrition: dialysis protein ~$1.0{-}1.3\ g/kg/day$; non-dialysis CKD protein ~$0.8\ g/kg/day$; PD protein ~$1.2{-}1.5\ g/kg/day$.