MedCram Lecture: Nephrotic vs. Nephritic Syndrome

Overview

• Nephrotic and nephritic syndromes are both conditions affecting the kidneys.
• Understanding their differences requires insight into their pathophysiology.
• Key Structures Involved:
  • Endothelial Cells: Surround the lumen of the vasculature.
  • Basement Membrane: Permeable layer allowing passage of small molecules.
  • Epithelial Cells (Podocytes): Form a sieve that usually prevents proteins from passing through.

Kidney Filtration Process

• Fluid moves from the vasculature through the endothelium and basement membrane, and into Bowman's space.
• Fluid that reaches Bowman's space is eventually excreted as urine unless reabsorbed.
• Pathway: Proximal convoluted tubule → Loop of Henle → Distal convoluted tubule → Collecting ducts → Urine.

Nephrotic Syndrome

• Cause: Dysfunction or loss of podocytes.
• Consequences:
  • Significant protein loss (3.5 grams/day or more).
  • Symptoms:
    • Frothy urine due to proteinuria.
    • Generalized edema due to protein loss (especially albumin).
    • Increased blood lipids as the liver compensates.
    • Hypercoagulable state (loss of antithrombin 3).
    • Risk of thrombosis, especially in the renal vein.
• Classification:
  • Primary nephrotic diseases: Directly affect the kidneys.
  • Secondary causes: Result from systemic diseases affecting the kidneys.

Nephritic Syndrome

• Cause: Immune complexes lodge in capillaries causing inflammation and damage.
• Consequences:
  • Inflammation attracts white blood cells and causes capillary damage.
  • Allows red and white blood cells and proteins to pass into the urine.
• Symptoms:
  • Hematuria (blood in urine).
  • Oliguria (reduced urine output) due to decreased glomerular filtration rate (GFR).
  • Hypertension due to reduced kidney function.
  • Presence of granular casts in urine.
• Classification:
  • Primary nephritic diseases: Directly affect the kidneys.
  • Secondary causes: Result from systemic diseases affecting the kidneys.

Key Differences

• Nephrotic Syndrome:
  • Mainly involves protein loss.
  • Less inflammatory.
  • High proteinuria without much cellular sediment.
• Nephritic Syndrome:
  • Involves inflammation and cellular debris.
  • Presence of blood and white cells in urine.
  • Often accompanies nephrotic-range proteinuria.

Conclusion

• Both syndromes can have primary or secondary causes, which will be discussed in more detail in future lectures.
• Key indicators help differentiate between the two syndromes based on urine analysis and symptoms.
• Understanding these differences is crucial for correct diagnosis and treatment.