M1. RENAL ANATOMY AND PHYSIOLOGY

• Kidney:

  • Retroperitoneal organ that weighs 150 grams and is 12.5 x 6 x 2.5 cm
• Ureter:

  • 25 cm long
• Bladder:

  • A nerve reflex is initiated when 150 mL of urine is accumulated in the bladder
• Urethra:

  • ♀️ women: 4cm (more prone to UTI because of faster travel time of bacteria)
  • ♂️ men: 24 cm
• Urine:

  • Fluid biopsy of the kidney
  • The biopsy of the kidney is nephron
• Nephron:

  • Regulates the selective clearance of waste from the blood by the kidneys while managing water and electrolyte balances
  • There are 1 to 1.5 million nephrons per kidney, totaling about 2-3 million nephrons
  • 2 types of nephrons:
  • Cortical: Found in the cortex, 85%, responsible for waste removal and nutrient reabsorption
  • Juxtamedullary: Primary function is the concentration of urine
• Renal Functions:

  1. Renal Blood flow

  2. Glomerular Filtration

  3. Tubular Reabsorption

  4. Tubular Secretion
• The kidney receives 25% of the total cardiac output

  Total Renal Blood Flow: 1200 mL/min

  Total Renal Plasma Flow: 600-700 mL/min
• Order of Urine Formation:

  • Glomerulus
  • Proximal Convoluted Tubules (PCT) - near
  • Loop of Henle (Ascending: active | Descending: passive)
  • Distal Convoluted Tubules (DCB) - far
  • Collecting Duct (where the final concentration of urine takes place)
  • Calyx
  • Renal Pelvis
• Glomerulus:

  • The “working portion” of the kidney
  • Coil of approx 8 capillary lobes (capillary tuft)
  • Located in Bowman’s capsule
  • Non-selective filter of plasma substances with MW of < 70,000 Daltons (Da)
  • Filtration diaphragm is found between the podocytes of Bowman’s space
• Tubular Reabsorption:

  • 1st function to be affected in renal disease
  • Body cannot lose 120 mL of water containing essential substances every minute
  • Renal Threshold: plasma concentration at which active transport stops
  • Glucose → renal threshold of 160 to 180 mg/dL