10.1 Pathophysiology of Acute and Chronic Kidney Disease

Kidney disease can wreak havoc on your body. From filtering blood to balancing electrolytes, your kidneys play a crucial role in keeping you healthy. When they start to fail, it affects everything from your bones to your blood.

Acute kidney injury happens suddenly, while chronic kidney disease develops over time. Both can lead to serious complications if left untreated. Understanding the causes, symptoms, and management of kidney disease is key to maintaining your health.

Kidney Function and Structure

Glomerular Filtration and Nephron Structure

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• Glomerular filtration rate (GFR) measures kidney function by assessing how much blood passes through glomeruli per minute
• Normal GFR ranges from 90-120 mL/min/1.73 m²
• Nephrons function as the basic structural and functional units of the kidney
• Each kidney contains approximately 1 million nephrons
• Nephron structure includes glomerulus, proximal tubule, loop of Henle, and distal tubule
• Glomerulus filters blood, while tubules reabsorb and secrete substances

Electrolyte Balance and Acid-Base Regulation

• Kidneys maintain electrolyte balance by regulating sodium, potassium, calcium, and phosphate levels
• Sodium regulation influences blood pressure and fluid balance
• Potassium balance affects muscle and nerve function
• Calcium and phosphate homeostasis impacts bone health
• Metabolic acidosis occurs when kidneys fail to excrete sufficient acid or reabsorb enough bicarbonate
• Symptoms of metabolic acidosis include rapid breathing, confusion, and fatigue
• Kidneys compensate for metabolic acidosis by increasing bicarbonate reabsorption and ammonium excretion

Acute and Chronic Kidney Disease

Acute Kidney Injury and Its Causes

• Acute kidney injury (AKI) involves sudden decline in kidney function over hours to days
• AKI classified into prerenal (decreased blood flow), intrinsic (damage to kidney tissue), and postrenal (urinary tract obstruction) causes
• Common causes of AKI include severe dehydration, sepsis, and nephrotoxic medications (NSAIDs, aminoglycosides)
• AKI diagnosis based on elevated serum creatinine, decreased urine output, or both
• Treatment focuses on addressing underlying cause and supporting kidney function

Chronic Kidney Disease Progression and Management

• Chronic kidney disease (CKD) characterized by gradual loss of kidney function over months to years
• CKD stages defined by GFR and presence of kidney damage markers (proteinuria)
• Stage 1: GFR ≥ 90 mL/min/1.73 m² with evidence of kidney damage
• Stage 2: GFR 60-89 mL/min/1.73 m²
• Stage 3: GFR 30-59 mL/min/1.73 m²
• Stage 4: GFR 15-29 mL/min/1.73 m²
• Stage 5: GFR < 15 mL/min/1.73 m² or dialysis (End-stage renal disease)
• End-stage renal disease (ESRD) requires renal replacement therapy (dialysis or kidney transplantation)
• Risk factors for kidney disease include diabetes, hypertension, obesity, and family history
• Management of CKD involves controlling blood pressure, managing diabetes, and dietary modifications

Complications of Kidney Disease

Urinary and Metabolic Abnormalities

• Proteinuria indicates kidney damage and increased risk of CKD progression
• Microalbuminuria (30-300 mg/day) serves as an early marker of kidney disease
• Macroalbuminuria (> 300 mg/day) suggests more advanced kidney damage
• Azotemia refers to elevated blood urea nitrogen (BUN) and creatinine levels
• Uremia results from accumulation of waste products in blood due to kidney failure
• Uremic symptoms include nausea, vomiting, fatigue, and altered mental status

Bone and Hematologic Complications

• Renal osteodystrophy encompasses bone disorders associated with CKD
• Altered vitamin D metabolism and secondary hyperparathyroidism contribute to renal osteodystrophy
• Manifestations include osteomalacia, osteitis fibrosa, and adynamic bone disease
• Anemia in kidney disease primarily caused by decreased erythropoietin production
• Other factors contributing to anemia include iron deficiency and chronic inflammation
• Treatment of renal anemia involves erythropoiesis-stimulating agents and iron supplementation