Severe Proteinuria — Site of Degeneration

Severe proteinuria condition is encountered when degeneration occurs in:

Correct Answer: Glomerulus capillaries

Proteinuria (abnormal presence of protein in urine) in its severe form is caused by damage to the glomerular capillaries — specifically the glomerular filtration barrier.

Normal Glomerular Filtration Barrier

The glomerular filtration barrier has three layers that prevent large proteins from passing into filtrate:

• Fenestrated capillary endothelium — pores allow small molecules but restrict cells.
• Glomerular basement membrane (GBM) — negatively charged, repels negatively charged albumin.
• Podocytes with filtration slits — final size and charge barrier.

Why Glomerular Damage Causes Severe Proteinuria

• When glomerular capillaries are damaged (e.g., in glomerulonephritis, diabetes mellitus, amyloidosis) → the filtration barrier breaks down → large proteins like albumin pass freely into filtrate → appear in urine as proteinuria.
• In nephrotic syndrome, massive proteinuria (>3.5 g/day in humans) is the hallmark due to glomerular injury.
• PCT tubular damage causes mild protein leakage (tubular proteinuria), but not severe.