Concise Summary of Renal Physiology

Kidney Functions

  • Regulation of ECF / Plasma Osmolarity: Water balance
  • Regulation of ECF / Plasma Volume: Na extsuperscript{+} & Cl extsuperscript{-} content
  • Regulation of Ion Concentrations: K extsuperscript{+}, Ca extsuperscript{2+}, HPO extsubscript{4} extsuperscript{2-}
  • Regulation of pH: [H extsuperscript{+}] via [HCO extsubscript{3} extsuperscript{-}]
  • Elimination of Waste: Urea, uric acid, creatinine, drugs, and metabolites

Nephron Structure

  • Functional Unit of Kidney: Nephron (approx. one million in each kidney)
  • Composed of:
    • Renal corpuscle
    • Renal tubule
  • Types of Nephrons:
    • Juxtamedullary nephrons (long loops of Henle)
    • Cortical nephrons (proximal & distal tubules in cortex)

Renal Vasculature

  • Blood Flow Components:
    • Renal artery, afferent arterioles, glomerular capillaries, efferent arterioles, peritubular capillaries, venules, renal vein

Filtration Process

  • Formation of Ultrafiltrate:
    • Occurs in Bowman's capsule
    • Majority reabsorbed in proximal convoluted tubule (PCT)
    • Loop of Henle: Concentrates interstitial fluid
    • Regulation in distal convoluted tubule (DCT) & cortical collecting duct (CCD)
    • Water content regulated in medullary collecting duct (MCD)

Glomerular Filtration Rate (GFR)

  • Renal Blood Flow: ~20% of cardiac output (~1100 ml/min)
  • Renal Plasma Flow: 600 ml/min (assuming 45% hematocrit)
  • GFR Calculation: GFR = 125 ml/min (180 L/day)
  • Urine Flow: ~1.5 L/day (over 99% of ultrafiltrate reabsorbed)

Tubular Processes

  1. Glomerular Filtration
  2. Tubular Secretion
  3. Tubular Reabsorption

Excretion Formula

  • Amount Excreted:
    • Amt excreted = filtered - reabsorbed + secreted
  • Clearance Concepts:
    • Substance X: Cleared from plasma
    • Substance Z: Fully recovered from filtrate