Kidney Structure and Function Quiz

Kidney Structure

• The functional unit of the kidney is the nephron.
• There are 1.2 million nephrons per kidney.
• The glomerulus is a network of capillaries within Bowman's capsule.
• Blood flows through the glomerulus and filters out wastes and water into the tubule.

Nephron Function

• The nephron forms a protein-free filtrate.
• The nephron regulates the filtrate to maintain fluid volume, electrolytes, and pH.

Renal Blood Flow

• Glomerular Filtration Rate (GFR) is the rate at which the glomeruli filter blood.
• Normal GFR is 87-139 mL/minute.
• Creatinine clearance is the most accurate measure of GFR.
• Creatinine is filtered by the glomeruli but not reabsorbed.
• Creatinine is a waste product of skeletal muscles.
• The higher the blood creatinine level, the lower the estimated GFR.

Urinary Structures

• Ureters transport urine from the kidneys to the bladder.
• The bladder is a muscular container that holds urine (300-500 mL).
• The urethra is a narrow passageway from the bladder to the outside of the body.
• The urethra has internal and external sphincters.
• Females have a 3-4 cm long urethra, while males have 18-20 cm.

Urine Composition

• Normal urine is clear yellow or amber in colour.
• Cloudiness may indicate the presence of bacteria, cells, or high solute concentration.
• Urine pH ranges from 4.6 - 8.0, but is normally acidic.
• Normal urine does not contain glucose or blood cells, and only occasionally contains trace protein.
• A healthy human should produce 0.5-1 cc of urine/kg per hour (average 30 cc/hr).

Kidney Functions

• Maintaining fluid and electrolyte concentration.
• Maintaining acid-base balance.
• Detoxifying the blood and eliminating wastes.
• Regulating blood pressure.
• Aiding RBC production.
• Regulating vitamin D and calcium formation.

Hormones and Renal Function

• Antidiuretic hormone (ADH) alters the tubules’ permeability to water.
  • Increased ADH leads to concentrated, low-volume urine.
  • Decreased ADH leads to less concentrated, high-volume urine.
• Aldosterone regulates water and sodium reabsorption.
  • Increased aldosterone increases H2O & Na reabsorption.
  • Decreased aldosterone promotes H2O & Na reabsorption.
• Renin is secreted in response to decreased extracellular volume.
• Vitamin D is converted to its active form in the kidneys for calcium and phosphate absorption.
• Erythropoietin stimulates RBC production when there is decreased oxygen to the kidney.

Tests of Renal and Bladder Function

• Renal Function Tests:
  • Blood Studies:
    • BUN: Blood Urea Nitrogen, measures urea which is a cellular waste product removed from the blood.
    • Creatinine: Waste product of skeletal muscles.
    • Electrolytes (K+, Na+).
  • Glomerular Filtration Rate (GFR).
    • GFR < 60 indicates renal injury.
  • Urinalysis:
    • Appearance: Colour, turbidity (cloudiness), pH, specific gravity, blood.
    • Microscopic Urine: bacteria, RBC, WBC, crystals, fat, casts.
    • Urinary Chemistry: bilirubin, ketones, glucose, sodium, potassium, protein.
• Bladder Function Tests:
  • Cystometry: measures bladder pressure using a pressure-measuring catheter.
  • Uroflowmetry: measures the time it takes to empty a full bladder.
  • Post Void Residual (PVR): measures residual urine in the bladder after voiding (usually with US--bladder scanner).>200ml is abnormal.
  • Direct visualization tests:
    • Cystoscopy: camera inserted through the urethra and visualizes the interior of the bladder.
    • Ureteroscopy: camera inserted through the urethra and bladder directly into the ureter to visualize the upper urinary tract.

Age-Related Renal Function

• Pediatric
  • Decreased ability to remove excess water and solutes.
  • Decreased concentrating ability.
  • Narrow margin for fluid and electrolyte balance.
  • Increased risk of medication toxicity.
• Geriatric
  • Decrease in renal blood flow and GFR.
  • Altered sodium and water balance.
  • Number of nephrons decrease due to renal vascular and perfusion changes.
  • Response to acid-base changes delayed.
  • Increased risk for medication toxicity.
  • Alterations in thirst and water intake.