Histology · Methods and stains
Electron microscopy: what it shows that light can't !
- Technique
It uses electrons instead of light and shows structures far smaller than light can, such as membranes, ribosomes and the inside of cilia.
Updated 2026-11-01
See it in 3D: Kidneys · Main bronchi
What it is
Electron microscopy resolves objects about 1 nanometre apart, against about 200 nanometres for light microscopy. Transmission EM (TEM) shows the inside of the cell in ultrathin sections; scanning EM (SEM) shows surfaces in relief. Clinically it is decisive in kidney biopsies, cilia, some tumours and viruses.
Key facts
- Usual fixation: glutaraldehyde followed by osmium tetroxide, which preserves and contrasts lipid membranes.
- Embedding in epoxy resin and ultrathin sections tens of nanometres thick.
- Contrast with heavy-metal salts (lead, uranium): the image is black and white.
- Electron-dense = dark (binds much metal); electron-lucent = pale.
Structure
- On TEM the cell membrane appears as a trilaminar line (dark-light-dark).
- RER appears as flattened cisterns studded with ribosomes; the Golgi as stacked curved sacs with vesicles.
- Mitochondria show a double membrane with inner cristae; lysosomes appear as dense bodies with mixed contents.
What electron microscopy adds
| Ultrastructural finding | Where | Meaning |
|---|---|---|
| Diffuse effacement of podocyte foot processes | Renal glomerulus | Minimal change disease (near-normal on light microscopy) |
| Subepithelial or subendothelial electron-dense deposits | Glomerular basement membrane | Immune-complex glomerulonephritis |
| Thinned or split glomerular basement membrane | Renal glomerulus | Alport syndrome and thin basement membrane disease |
| Missing or defective axonemal dynein arms | Respiratory cilia | Primary ciliary dyskinesia |
| Birbeck granules (tennis-racket shaped) | Langerhans cells | Langerhans cell histiocytosis |
| Dense-core neurosecretory granules | Tumour cells | Neuroendocrine origin of a tumour |
| Abnormal cristae or increased mitochondria | Muscle | Mitochondrial disease |
Test yourself
Think of the answer, then tap the question to see it.
Which electron microscopy finding defines minimal change disease?
Diffuse effacement of podocyte foot processes, with glomeruli that look almost normal on light microscopy.
What does it mean that a structure is electron-dense?
It holds a lot of the heavy-metal contrast and blocks electrons, so it looks dark.
Which tennis-racket shaped structure identifies Langerhans cells?
The Birbeck granule, seen with electron microscopy.
Why does the electron microscope resolve more detail than the light microscope?
Electrons have a much shorter wavelength than visible light, so objects about 1 nm apart can be separated.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Microscopy and stains: H&E, PAS, trichrome, silver, immunohistochemistry
- From biopsy to slide: fixation, sectioning, frozen section
- Cilia, microvilli and stereocilia
- Glomerulus and the filtration barrier: podocytes, mesangium, JGA
- Organelles: nucleus, ER, Golgi, mitochondria, lysosomes, peroxisomes
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: Tissue preparation 9 (Digital Histology, 2024); Stains 3 (Digital Histology, 2024); Tissue preparation 1 (Digital Histology, 2024).
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Representative model, for educational purposes only.