Urinary System: Structure, Function, Disorders, and Clinical Assessment

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Urinary System Overview and Anatomy

Functions of the Urinary System

The urinary system is essential for maintaining internal balance by removing waste and regulating fluid and electrolyte levels.

Excretion: Removes metabolic wastes, hormones, drugs, and foreign substances from the blood.
Regulation: Controls water, electrolytes, and acid-base balance.
Hormone Secretion: Produces erythropoietin (stimulates red blood cell production), activates vitamin D, and regulates blood pressure via the renin-angiotensin-aldosterone system (RAS).
Clinical Note: Kidney failure can cause anemia due to reduced erythropoietin and may require medication dose adjustments.

Anatomy and Gross Location

The urinary system consists of the kidneys, ureters, urinary bladder, and urethra.

Kidneys: Filter blood and form filtrate; located under the ribs.
Ureters: Small tubes carrying urine from each kidney to the bladder.
Urinary Bladder: Collects urine; sits low in the pelvis.
Urethra: Urine exits the body.

Kidney Structure and Nephrons

Nephrons are the functional units of the kidney, responsible for filtration and urine formation.

Nephron Components: Renal corpuscle (glomerulus + Bowman capsule), proximal convoluted tubule, loop of Henle, distal convoluted tubule, collecting duct.
Renal Anatomy: Cortex, medulla, pyramids, calyces, and ureter.
Clinical Note: Filtration, reabsorption, and urine abnormalities are key for exam questions.

Urine Formation, Reabsorption, and Kidney Blood Flow

Formation of Urine

Urine formation involves filtration, reabsorption, and secretion within the nephron.

Filtration: Occurs in the glomerulus; fluid and small solutes move into Bowman capsule, forming filtrate.
Reabsorption: Returns needed water, nutrients, and electrolytes to blood.
Volume: About 180 L of plasma filtered daily; most is reabsorbed, preventing dehydration.
Clinical Note: Low blood pressure reduces glomerular filtration and urine output.

Reabsorption Mechanisms

Reabsorption occurs mainly in the tubules, using active transport and osmosis.

Proximal Tubule: Reabsorbs most water, glucose, nutrients, and electrolytes.
Loop of Henle: Descending limb allows water out by osmosis; ascending limb pumps sodium and chloride out.
Distal Tubule & Collecting Duct: Water reabsorption depends on body needs; increased permeability during dehydration.
Glucosuria: High blood glucose leads to glucose in urine, indicating poor control.

Hormonal Regulation of Reabsorption

Several hormones influence reabsorption in the nephron.

Antidiuretic Hormone (ADH): Promotes water reabsorption in distal tubule and collecting duct.
Aldosterone: Supports sodium and fluid retention.
Atrial Natriuretic Hormone: Reduces sodium and fluid reabsorption.

Blood Flow Through the Kidney

Blood enters the kidney via the renal artery, passes through afferent arteriole to glomerulus, and exits via efferent arteriole.

Afferent Arteriole: Carries blood to glomerulus.
Efferent Arteriole: Carries blood away from glomerulus.
Renal Blood Flow: Receives about 25% of cardiac output.

Glomerular Filtration Rate (GFR)

GFR measures the rate of filtration in the kidneys and is a key indicator of renal function.

Normal GFR: Greater than 90 mL/min.
Arteriolar Tone: Afferent constriction decreases GFR; dilation increases GFR. Efferent constriction increases GFR.
Sympathetic Activation: Causes vasoconstriction, lowering GFR.
Clinical Note: GFR is used to assess kidney failure; low GFR does not always indicate acute injury.

Change	Pressure/Flow Result	Filtrate Result
Afferent constriction	Less blood enters glomerulus	Decreases
Afferent dilation	More blood enters glomerulus	Increases
Efferent constriction	Pressure builds behind narrowed exit	Increases

Composition of Blood, Filtrate, and Urine

Filtration and reabsorption determine the final composition of urine.

Filtered Volume: 180 L/day; only 1.4 L becomes urine.
Normal Urine: No glucose, no protein (or only trace), high potassium, and conserved bicarbonate.
Clinical Note: Protein or glucose in urine indicates abnormal permeability or poor blood-glucose control.

Incontinence, Retention, and Diagnostic Assessment

Incontinence and Enuresis

Incontinence is the loss of voluntary bladder control; enuresis is involuntary urination in children beyond the expected age.

Stress Incontinence: Leakage with increased abdominal pressure; more common in women.
Overflow Incontinence: Bladder overfills and leaks; may occur in older adults or with neurologic injury.

Urinary Retention

Retention is incomplete emptying of the bladder, sometimes with overflow leakage.

Assessment: Bladder scanner estimates retained volume; catheterization may be needed if retention is significant.
Minimum Output: 30 mL/hour is the action threshold; less than this over time requires clinical attention.

Urinalysis: Appearance and Constituents

Urinalysis evaluates urine for color, odor, and abnormal substances.

Appearance: Color varies with intake, medications, and foods; odor is not definitive for diagnosis.
Abnormal Constituents: Blood, protein, bacteria, casts, glucose, and ketones may indicate trauma, infection, or poor glucose control.

Blood Tests and Other Diagnostics

Blood tests and imaging assess kidney function and structure.

Serum Creatinine: Rises with reduced filtration; primary test for kidney damage.
BUN: Indicates nitrogen waste accumulation.
Metabolic Acidosis: Occurs when kidneys fail to maintain acid-base balance.
Urine Culture: Identifies infection and guides antibiotic choice.
Cystoscopy: Scope used to view bladder and lower urinary tract.

Diuretics and Dialysis

Diuretic Drugs

Diuretics increase removal of sodium and water; some affect potassium handling.

Lasix (Furosemide): Linked with potassium loss.
Spironolactone: Acts on aldosterone pathway.
Clinical Note: Know overall effect and electrolyte relationship; site of action is not required for this course.

Dialysis

Dialysis replaces kidney filtration in failure; two main types are hemodialysis and peritoneal dialysis.

Hemodialysis: Blood is filtered by a machine via fistula/graft; 3-4 hours, 3-4 times weekly.
Peritoneal Dialysis: Sterile fluid in peritoneal cavity exchanges waste; often overnight for about 10 hours.
Clinical Note: Dialysis is life-sustaining in chronic failure; can be temporary in acute injury.

Type	Mechanism	Duration
Hemodialysis	Blood filtered by machine	3-4 hours, 3-4 times/week
Peritoneal Dialysis	Fluid exchanges waste in peritoneal cavity	~10 hours overnight

Urinary Tract Infections (UTIs)

Overview

UTIs are infections of the urinary system, commonly bacterial, and more frequent in women.

Lower UTIs: Urethritis and cystitis.
Upper UTIs: Pyelonephritis (kidney infection).
Risk Factors: Shorter urethra in women, retained urine, reflux, and obstruction.

Cystitis and Urethritis

Inflammation/infection of bladder (cystitis) or urethra (urethritis) presents with urinary symptoms.

Symptoms: Dysuria, urgency, frequency, nocturia, cloudy/odorous urine, bacteriuria, pyuria, microscopic hematuria.
Systemic Findings: Fever, malaise, nausea, leukocytosis.
Older Adults: May present with confusion.

Pyelonephritis

Pyelonephritis is infection/inflammation of the kidneys, often ascending from the bladder.

Symptoms: CVA tenderness, abnormal urine findings.
Vesicoureteral Reflux: Backward urine flow increases infection risk.

Treatment of UTIs

Antibiotics: Mainstay of UTI treatment.

Inflammatory Disorders

Glomerulonephritis

Glomerulonephritis is inflammation of the glomeruli, increasing permeability and reducing filtration.

Urine Findings: Proteinuria, hematuria, erythrocyte casts, dark/cloudy urine.
Blood Findings: Elevated BUN/creatinine, metabolic acidosis.
Symptoms: Edema (especially facial/periorbital), high blood pressure, decreased urine output, flank/back pain.
Treatment: Restrict sodium, protein, and fluid as needed; medication per clinical problem.

Nephrotic Syndrome

Nephrotic syndrome involves heavy protein loss due to increased glomerular permeability.

Findings: Low albumin, heavy proteinuria, lipiduria, casts, massive edema, increased abdominal girth.
Comparison: Heavier protein loss and low albumin (no blood) distinguish nephrotic syndrome from glomerulonephritis.

Disorder	Key Findings
Glomerulonephritis	Proteinuria plus blood in urine; low protein; high BP; low urine output
Nephrotic Syndrome	Heavier protein loss; low albumin; lipiduria; massive edema; no blood

Urinary Tract Obstructions

Overview

Obstruction can occur at any level of the urinary tract and leads to urine backup and potential renal damage.

Causes: Stones, tumors, hypertrophy, scar tissue.
Postrenal Problem: Obstruction after the kidney affects outflow.

Urolithiasis / Renal Calculi

Urinary stones are most commonly composed of calcium; dehydration increases risk.

Types: Urolithiasis (urinary tract), nephrolithiasis (kidney).
Gout: May produce uric-acid stones.
Clinical Note: Calcium stones are most common.

Signs and Assessment

Symptoms: Small stones may be asymptomatic; obstructing stones cause severe pain and hematuria.
Obstruction: Causes urine backup and infection risk.
Stone Analysis: Strain urine to recover and analyze stone composition.

Treatment and Prevention

Small Stones: May pass naturally; increase fluid intake.
Prevention: Address stone material/cause; reduce excessive calcium if indicated.

Hydronephrosis

Hydronephrosis is fluid dilation of the kidney due to outflow obstruction.

Mechanism: Urine accumulates behind obstruction, raising pressure and infection risk.

Vascular, Congenital, and Tumor Disorders

Nephrosclerosis

Nephrosclerosis is thickening and hardening of renal arterioles, reducing blood supply and filtration.

Ischemia: Narrowed vessels cause tissue damage.

Congenital Disorders

Vesicoureteral Reflux: Backward urine flow increases infection risk.
Ectopic Kidney: Recognized as an anatomic variant.

Adult Polycystic Kidney Disease

An autosomal dominant disorder (chromosome 16) with multiple cysts replacing kidney tissue.

Progression: Asymptomatic until ~age 40; leads to chronic renal failure.

Wilms Tumor

Definition: Common kidney tumor in children; cancer potential.

Acute and Chronic Renal Failure

Acute Kidney Injury (AKI) / Acute Renal Failure (ARF)

AKI/ARF is sudden and potentially reversible if the cause is treated.

Findings: Elevated creatinine/BUN, fluid retention, electrolyte imbalance, acid-base disturbance.
Dialysis: May be used temporarily.
Locations: Prerenal (blood delivery), intrarenal (filtering tissue), postrenal (outflow obstruction).
Oliguria: Urine output <30 mL/hour; anuria is no urine production.

AKI Causes and Monitoring

Causes: Pyelonephritis, stones/obstruction, low blood pressure, nephrotoxic drugs, iodinated contrast.
Monitoring: Creatinine, BUN, urine output, electrolytes, acid-base status.

Chronic Renal Failure / Chronic Kidney Disease (CKD)

CKD is gradual, irreversible loss of kidney function, often asymptomatic early.

Stages: Defined by GFR; dialysis required in end-stage disease.
Urine Output: May persist even in advanced stages; does not guarantee adequate filtration.

Stage	GFR (mL/min)
1	90 or higher
2	60-89
3	30-60
4	15-30
5	Less than 15

Chronic Renal Failure: Early and Complete Failure

Early Compensation: Increased urine output despite declining filtration.
Symptoms: Nausea, anemia, fatigue, weight loss, elevated blood pressure.
Complete Failure: Oliguria/anuria, dry skin, bruising, anemia, azotemia, electrolyte imbalance.
Three As of End-Stage Disease: Azotemia, anemia, acidosis.

Key Equations and Values

Glomerular Filtration Rate (GFR):
Normal GFR:
Minimum Urine Output:

Summary Table: Disorders and Key Findings

Disorder	Key Findings
Glomerulonephritis	Proteinuria, hematuria, casts, edema, high BP
Nephrotic Syndrome	Heavy proteinuria, low albumin, lipiduria, massive edema
UTI	Dysuria, urgency, frequency, cloudy urine, bacteriuria
Renal Calculi	Pain, hematuria, obstruction, stone analysis
CKD	Low GFR, anemia, azotemia, acidosis, oliguria/anuria

Additional info: All content is based strictly on the professor's transcript and audited PowerPoint images. No outside clinical content was added. Testing boundaries and exam emphasis are noted where specified by the professor.