33 Patho

Disorders of Renal Function

Overview

The kidneys are susceptible to a variety of disorders, many of which share similarities with diseases affecting other body systems. These disorders can be congenital, infectious, obstructive, metabolic, or neoplastic in nature.

• Congenital defects: Includes renal agenesis/hypoplasia (kidney does not develop or is too small), polycystic kidney disease (inherited, multiple fluid-filled cysts), and structural anomalies (e.g., ureteropelvic junction obstruction).

• Infections: Urinary tract infections (UTIs) such as cystitis (bladder infection) and pyelonephritis (kidney infection).

• Inflammatory disorders: Glomerulonephritis (immune-mediated inflammation of glomeruli), interstitial nephritis (inflammation of kidney tissue, often from drugs).

• Obstructive disorders: Kidney stones, hydronephrosis (swelling due to backed-up urine), prostatic enlargement or strictures causing urinary obstruction.

• Metabolic disorders: Diabetic nephropathy (damage from chronic high blood sugar), amyloidosis (abnormal protein deposits), autoimmune diseases (e.g., lupus nephritis).

• Neoplasms: Renal cell carcinoma (most common kidney cancer), Wilms tumor (childhood kidney cancer).

Cystic Disease of the Kidney

Types and Pathophysiology

Cystic kidney diseases are characterized by the formation of fluid-filled sacs (cysts) in parts of the nephron, often due to blocked tubules and changes in the tubule wall.

• Simple or acquired renal cysts: Usually harmless, seen in adults.

• Medullary cystic disease: Small cysts in the kidney's inner part.

• Polycystic kidney disease (PKD): Many cysts form, kidneys enlarge.

• Autosomal recessive PKD: Rare, seen in infants/children.

• Autosomal dominant PKD (ADPKD): More common, mutations in PKD1 (85%) and PKD2 (15%) genes, manifests in adulthood.

ADPKD Cause: Abnormal growth of epithelial cells, tubule dilation, and formation of multiple fluid-filled cysts in both kidneys.

Urinary Tract Obstruction

Causes

Obstruction of the urinary tract can result from a variety of structural and functional abnormalities.

• Developmental defects: Structural abnormalities present at birth.

• Calculi (stones): Most common cause in adults.

• Pregnancy: Temporary but common uterus compression of ureters.

• Benign prostatic hyperplasia (BPH): Most common cause in older men.

• Tumors: Can occur inside or pressing on the urinary tract.

• Scar tissue: From infection, inflammation, or surgery.

• Neurologic disorders: E.g., spinal cord injury leading to neurogenic bladder.

Effects of Urinary Obstruction

• Urine stasis: Increases risk of infection and kidney stones.

• Back pressure: Pushes against kidney tissue, decreases blood flow, and causes kidney damage.

• Manifestations: Depend on location, cause, and speed of development. Common symptoms include pain, fever, urinary dysfunction (swelling, decreased urine output, increased creatinine/BUN).

Kidney Stones

Formation and Types

Kidney stones are hard, crystal-like structures formed from substances in urine. Their formation requires a nidus (starting point) and urine conditions that allow crystal growth.

• High concentration of stone-forming substances in urine.

• Ability to bind/cluster into stones.

• Lack of inhibitors (normally prevent stone growth).

Types of Kidney Stones:

• Calcium stones: Oxalate or phosphate.

• Struvite stones: Magnesium ammonium phosphate (linked to infection).

• Uric acid stones.

• Cystine stones: Rare, genetic.

Kidney Stone Treatment

Management and Diagnosis

• Dietary restriction: Avoid certain foods.

• Calcium supplements: Balance oxalate.

• Thiazide diuretics: Reduce calcium in urine.

• Cellulose phosphate: Binds calcium in gut.

• Pain relief: Medications for ureteral colic (radiating flank pain).

• Antibiotics: If infection is present.

• Stone removal methods: Ureteroscopic removal, percutaneous removal, extracorporeal lithotripsy (shock waves to break stones).

Diagnosis:

• Urinalysis (check for crystals, infection).

• Imaging tests: X-ray, IV pyelography, ultrasound.

Urinary Tract Infections (UTIs)

Types and Causes

• Asymptomatic bacteriuria: Bacteria present without symptoms.

• Symptomatic infections: Bacteria cause symptoms.

• Cystitis: Bladder infection (burning, frequency, urgency).

• Pyelonephritis: Kidney infection (fever, flank pain, dysuria).

Common Pathogens:

• Escherichia coli (E. coli): Most common cause.

• Staphylococcus saprophyticus: Some uncomplicated UTIs.

• Other gram-negative rods: Proteus mirabilis, Klebsiella pneumoniae, Enterobacter, Pseudomonas, Serratia (more common in complicated infections).

• Gram-positive cocci: Staphylococcus aureus, Group B streptococcus.

Risk Factors for UTIs Associated with Stasis

• Structural obstructions: Kidney/urinary stones, enlarged prostate, pregnancy, ureter-bladder junction malformation.

• Functional (nerve/muscle) problems: Neurogenic bladder, infrequent urination, unstable bladder muscle contractions, constipation.

Protective Mechanisms Against UTIs

• Washout phenomenon: Urination flushes bacteria.

• Mucin layer: Protective coating on bladder lining.

• Local immune defenses: Body's immune system fights bacteria.

• Normal flora (women): Healthy bacteria block harmful bacteria.

• Prostate secretions (men): Antibacterial properties prevent infection.

Special Considerations in UTI Patients

• Sexually active women: Higher risk due to shorter urethra and sexual activity.

• Pregnant women: Hormonal changes and pressure on bladder increase risk.

• Infants: May present with fever, irritability, poor feeding.

• Toddlers: Often show nonspecific signs (fever, accidents, irritability).

• Adolescents: Linked to sexual activity and hygiene.

• Adults: Usually show classic UTI symptoms.

• Elderly: May have confusion, weakness, or falls instead of typical urinary symptoms.

Diagnosis and Treatment of UTIs

• Diagnosis: Based on symptoms, examination, and urine tests for microorganisms. Imaging (X-ray, ultrasound, CT, renal scan) may be used to identify contributing factors.

• Treatment: Based on the pathogen causing the infection.

Glomerulonephritis

Definition and Manifestations

Glomerulonephritis is inflammation of the glomeruli, the tiny kidney filters. It can cause urinary and systemic changes.

• Proteinuria: Protein in urine (foamy urine).

• Hematuria: Blood in urine due to capillary wall damage (red or brown urine).

• Pyuria: Pus in urine (infection/inflammation).

• Oliguria: Low urine output.

• Edema: Swelling (face, hands, feet).

• Hypertension: High blood pressure due to fluid and sodium retention.

• Azotemia: Buildup of waste products in blood (increased BUN, creatinine).

Causes

• Post-streptococcal infection: Immune reaction after strep throat.

• Autoimmune diseases: Lupus.

• Other infections: Hepatitis, endocarditis.

Types of Glomerular Diseases

• Acute glomerulonephritis: Sudden inflammation after infection.

• Progressive glomerulonephritis: Loss of kidney function, severe form.

• Nephrotic syndrome: Heavy proteinuria, swelling, low blood protein.

• Membranous glomerulonephritis: Thickened membrane, cases of nephrotic syndrome.

• Minimal change disease: Common in children, proteinuria but normal kidney structure.

• Focal segmental glomerulosclerosis (FSGS): Scarring in parts of some glomeruli, leads to chronic kidney failure.

• IgA nephropathy (Berger's disease): IgA deposits in glomeruli after infections, causes blood in urine.

• Chronic glomerulonephritis: Ongoing inflammation and scarring, chronic kidney failure.

Tubulointerstitial Disorders

Types and Pathophysiology

• Acute tubular necrosis (ATN): Sudden death of tubular cells, usually from ischemia or toxins. Findings: oliguria, dark/muddy urine, increased creatinine, fluid retention.

• Renal tubular acidosis (RTA): Tubules can't secrete acid or reabsorb bicarbonate, causing metabolic acidosis. Findings: metabolic acidosis, weakness, bone pain, kidney stones.

• Acute interstitial nephritis: Bacterial infection of kidney tubules and interstitium. Findings: fever, chills, flank pain, dysuria, cloudy urine, CVA tenderness.

• Toxin effects: Tubular damage from drugs or chemicals. Findings: hematuria, decreased urine output, toxin exposure history.

Summary Table: Types of Kidney Stones

Type	Main Composition	Associated Factors
Calcium stones	Oxalate or phosphate	Hypercalciuria, diet
Struvite stones	Magnesium ammonium phosphate	Urinary tract infection
Uric acid stones	Uric acid	Gout, high purine diet
Cystine stones	Cystine	Genetic disorder

Summary Table: Common Pathogens in UTIs

Pathogen	Type of UTI
Escherichia coli	Most uncomplicated and complicated UTIs
Staphylococcus saprophyticus	Some uncomplicated UTIs
Other gram-negative rods	Complicated UTIs
Gram-positive cocci	Complicated UTIs

Key Equations

• Glomerular Filtration Rate (GFR): $GFR = \frac{U_{inulin} \times V}{P_{inulin}}$

• Renal Clearance: $C_x = \frac{U_x \times V}{P_x}$

Additional info: Some details have been expanded for clarity and completeness, including definitions, examples, and tables for stone types and UTI pathogens.