Glomerulus and the filtration barrier: podocytes, mesangium, JGA !
- Organ
The glomerulus is a tuft of capillaries that filters blood; its three-layer barrier lets water and salts through but holds back proteins.
Updated 2026-11-01
See it in 3D: Kidneys
What it is
The renal corpuscle is a tuft of capillaries, the glomerulus, between the afferent and efferent arterioles, wrapped by Bowman's capsule. The filtration barrier has three layers: fenestrated endothelium, glomerular basement membrane and slit diaphragms between podocyte foot processes. Nearly every glomerular disease is explained by the layer that is damaged, which makes it a core exam topic.
Structure
- On H&E: a rounded tuft of capillaries surrounded by Bowman's space and the flat parietal layer of the capsule.
- Vascular pole: the arterioles enter and leave here; the macula densa sits against it, a cluster of tall cuboidal cells with crowded nuclei.
- Urinary pole: Bowman's space continues into the proximal tubule.
- PAS or silver stains outline the basement membrane; electron microscopy shows foot processes and where immune deposits sit.
Function
- Makes the glomerular filtrate, an ultrafiltrate of plasma without cells or large proteins.
- The different calibre of afferent and efferent arterioles keeps pressure high inside the tuft.
- The macula densa and juxtaglomerular cells adjust filtration and release renin, which starts the renin-angiotensin-aldosterone system.
Barrier layers and what happens when they fail
| Component | What it is like | Typical disease |
|---|---|---|
| Endothelium | Fenestrated capillary with a negative glycocalyx | Thrombotic microangiopathy (hemolytic uremic syndrome) |
| Glomerular basement membrane | Thick sheet of type IV collagen, laminin and heparan sulfate | Alport syndrome (abnormal type IV collagen); anti-GBM disease (Goodpasture) |
| Podocytes | Cells with interdigitating foot processes joined by the slit diaphragm | Minimal change disease and focal segmental glomerulosclerosis (foot process effacement) |
| Mesangium | Contractile, phagocytic cells in a matrix between capillaries | IgA nephropathy (mesangial deposits); nodules of diabetic nephropathy |
Markers
- PAS (basement membrane)
- Methenamine silver
- Immunofluorescence (IgA, IgG, C3)
- Electron microscopy
Clinical notes
- Nephrotic syndrome: podocyte or barrier damage with heavy proteinuria, edema and low albumin.
- Nephritic syndrome: glomerular inflammation with hematuria, red cell casts and hypertension; red cell casts point to glomerular bleeding.
- Prerenal acute kidney injury: if perfusion pressure falls, filtration falls even when the glomerulus is healthy.
Test yourself
Think of the answer, then tap the question to see it.
What are the three layers of the glomerular filtration barrier?
The fenestrated endothelium, the glomerular basement membrane and the slit diaphragm between podocyte foot processes.
Which electron microscopy finding defines minimal change nephrotic syndrome?
Diffuse effacement of podocyte foot processes, with near-normal light microscopy.
Which cells release renin, and where are they?
The juxtaglomerular cells, modified smooth muscle cells in the wall of the afferent arteriole.
What does the macula densa sense?
The sodium chloride reaching the end of the thick ascending limb and the start of the distal tubule; it uses that signal to adjust filtration and renin.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
Related conditions
Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice.
Sources: 25.4 Microscopic Anatomy of the Kidney (OpenStax, Rice University, 2022); 25.5 Physiology of Urine Formation (OpenStax, Rice University, 2022); Kidneys (National Cancer Institute, SEER Training Modules, 2026).
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Representative model, for educational purposes only.