Kidney Function and Disorders Quiz

Kidney Function and Disorders

• Kidney Weight: The combined weight of both kidneys represents approximately 0.5% of total body weight.

• Kidney Location: Kidneys span from the 12th thoracic to the 3rd lumbar vertebrae.

• Kidney Blood Flow: Kidneys receive approximately 20% of cardiac output.

• Nephron Count: Each kidney contains approximately 1 million nephrons.

• Glomerular Filtration Rate (GFR):

  • Male: Normal GFR is 120 +/- 25 mL/min using creatinine clearance.
  • Female: Normal GFR is 95 +/- 20 mL/min using creatinine clearance.

• Serum Creatinine: Normal range is 0.8 to 1.3 mg/dL.

• Serum Osmolality: Normal range is 280-290 mOsm/kg.

• Urine Osmolality:

  • Diluted Urine: 50-100 mOsm/kg
  • Concentrated Urine: 900-1200 mOsm/kg

• Tubular Reabsorption:

  • Proximal Convoluted Tubule (PCT): 67% of filtered load is reabsorbed.
  • Thick Ascending Loop of Henle: 25% of filtered load is reabsorbed.
  • Distal Convoluted Tubule (DCT): 5% of filtered load is reabsorbed.
  • Collecting Tubule: 3% of filtered load is reabsorbed.
  • Urine Production: 0.4% of filtered load remains as urine.

• Electrolyte Intake/Excretion:

  • Sodium: Normal daily intake and excretion is 80-250 mEq/day. Normal plasma concentration is 135-145 mEq/L.
  • Potassium: Normal plasma concentration is 3.5-5.0 millimoles. Normal intracellular potassium concentration is 135-145 millimoles. Average dietary potassium intake is 80-120 millimoles per day.

Kidney Function and Acid-Base Balance

• Hydrogen Ion Excretion: Kidneys excrete 50-100 milliequivalents of hydrogen ions per day.
• Acid-Base Range: 6.8 to 7.8 pH range compatible with survival. 16 to 120 nanoequivalents per liter hydrogen concentration range is compatible with survival.
• Minimum Urine pH: 4.5.
• CO₂ Production: Approximately 15,000 millimoles of CO2 are produced daily.
• Non-carbonic Acid Production: Approximately 50-100 milliequivalents of non-carbonic acids are produced daily.

Kidney Function and Volume Balance

• Normal Urine Output: 0.5 mL/kg/hour.
• Blood Urea Nitrogen (BUN): Normal range is 6-20 mg/dL.
• Acute Kidney Injury (AKI) Criteria:
  • Serum Creatinine: Increase of 0.3 mg/dL within 48 hours. 50% increase in serum creatinine compared to baseline within 7 hours.
  • Urine Output: Less than 0.5 mL/kg/hr for 6 hours.

Kidney Function and Chronic Kidney Disease (CKD)

• Chronic Kidney Disease (CKD) Stages: GFR determines CKD stage
  • Stage 1 CKD: GFR >90 mL/min/1.73m²
  • Stage 2 CKD: GFR 60-89 mL/min/1.73m²
  • Stage 3 CKD: GFR 30-59 mL/min/1.73m²
  • Stage 4 CKD: GFR 15-29 mL/min/1.73m²
  • Stage 5 CKD: GFR <15 mL/min/1.73m²

Kidney Function and Fluid Balance

• Body Fluid Compartments:
  • Intracellular Fluid (ICF): 2/3 of total body water.
  • Extracellular Fluid (ECF): 1/3 of total body water.
    • Intravascular Fluid: 1/4 of ECF.
    • Interstitial Fluid: 3/4 of ECF.

Electrolyte Disorders

• Hyponatremia: Plasma sodium concentration below 135 mEq/L. Urine osmolality below 100 mOsm/kg in primary polydipsia. Urine sodium usually above 40 mEq/L in SIADH.
• Hypernatremia: Plasma sodium concentration above 145–147 mEq/L.
• Ideal Body Weight (IBW):
  • Male: 50 kg + 2.3 kg for each inch over 5 feet.
  • Female: 45.5 kg + 2.3 kg for each inch over 5 feet.
• Adjusted Body Weight (AdjBW): IBW + 0.4 x (TBW-IBW)