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PH-RN04

Nephritic syndrome

How immune-mediated inflammation of the glomeruli lets red cells into the urine and lowers filtration, causing haematuria with red-cell casts, salt retention, high blood pressure and oedema.

By the end, you can

  • Describe how antibodies and immune complexes injure the glomerulus and recruit inflammatory cells.
  • Explain how red cells reach the urine and why red-cell casts place the bleeding in the nephron.
  • Explain why a falling GFR with intact tubules causes salt and water retention, hypertension and oedema.
  • Contrast the nephritic and nephrotic patterns in mechanism and findings.
  • Recognise the classic biopsy, urine and lung findings, classifications and tests of nephritic syndrome, and explain how its main treatments act on the mechanism.

What it is

Nephritic syndrome is the pattern produced by inflammation of the glomeruli (glomerulonephritis): blood in the urine with red-cell casts, a reduced GFR, retention of salt and water with hypertension and oedema, and usually moderate proteinuria. Its causes are mostly immune and range from a self-limiting reaction after infection to rapidly progressive disease.

4 types to tell apart
Immune-complex glomerulonephritis
Antigen–antibody complexes deposit or form in the glomerulus: after streptococcal or other infections, as IgA in the mesangium (IgA nephropathy) or in lupus nephritis. Complement is often consumed.
Anti-GBM disease
Antibodies target type IV collagen in the glomerular basement membrane; the same antibodies can attack the lung’s alveolar basement membrane.
ANCA-associated (pauci-immune) glomerulonephritis
Few deposits are seen. Antibodies against neutrophil enzymes activate neutrophils, which injure small vessels, including glomerular capillaries.
Rapidly progressive (crescentic) glomerulonephritis
Severe injury from any of these causes, with crescents filling the capsular space and loss of function over days to weeks.

US spelling: oedema → edema.

Normal function

A glomerulus keeps cells in the blood

Each is a tuft of capillary loops held together by mesangial cells, which support the loops and clear trapped debris. Blood arrives through the and leaves through the ; filtrate collects inside the , whose outer wall is lined by flat parietal epithelial cells.

The filtration barrier lets water and small solutes through but holds back red cells and almost all protein, so healthy urine contains very few red cells. Because the glomerulus receives a large blood flow and filters plasma under pressure, antibodies and immune complexes in the blood reach it in quantity, and some can lodge in its walls.

The release renin when glomerular perfusion falls, and the tubules adjust sodium reabsorption to the amount filtered.

Point to it on the model