Basement membrane !
- Tissue
A thin sheet of proteins under every epithelium that anchors it to the tissue below and acts as a filter and a barrier.
Updated 2026-11-01
What it is
The basement membrane is a layer of extracellular matrix that separates epithelium (and also endothelium, muscle cells, fat cells and Schwann cells) from connective tissue. It holds the cells in place, guides their polarity and repair, and controls what passes between epithelium and the blood. When cancer cells cross it, a carcinoma in situ becomes invasive.
Structure
- Basal lamina (seen with electron microscopy): lamina lucida and lamina densa, built mainly of type IV collagen, laminin, nidogen and perlecan (a heparan sulfate proteoglycan), made by the epithelial cells.
- Reticular lamina: type III (reticular) collagen fibres made by the connective tissue underneath; type VII collagen anchoring fibrils tie it down in the skin.
- On H&E it is barely visible; PAS stains it magenta and silver stains outline it, which is why it shows up well in glomeruli.
- Epithelial cells attach to it through hemidesmosomes and integrins.
Function
- Anchors epithelium to connective tissue.
- Selective filter: in the glomerulus it is part of the filtration barrier.
- Scaffold for cell migration during wound repair and regeneration.
- Barrier: separates epithelium from vessels; crossing it defines invasion.
Markers
- PAS positive
- Type IV collagen
- Laminin
- Silver (Jones) stain
Clinical notes
- Alport syndrome: inherited defects of type IV collagen thin and split the glomerular basement membrane, with hematuria, hearing loss and eye changes.
- Goodpasture (anti-GBM) disease: antibodies against type IV collagen attack glomerular and alveolar basement membranes.
- Bullous pemphigoid: antibodies against hemidesmosome proteins split the skin at the basement membrane zone, giving tense blisters.
- Diabetes thickens capillary and glomerular basement membranes.
- Carcinoma in situ stays above an intact basement membrane; invasive carcinoma breaks through it.
Test yourself
Think of the answer, then tap the question to see it.
Which collagen type forms the network of the basal lamina?
Type IV collagen, together with laminin, nidogen and perlecan.
What stain makes the basement membrane stand out on light microscopy?
PAS (periodic acid–Schiff), which stains its carbohydrate-rich glycoproteins magenta; silver stains also outline it.
What distinguishes carcinoma in situ from invasive carcinoma?
In carcinoma in situ the malignant cells stay above an intact basement membrane; in invasive carcinoma they have crossed it into the connective tissue.
Which junctions attach basal epithelial cells to the basement membrane?
Hemidesmosomes, which use integrins to bind laminin in the basal lamina.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Epithelium: classification (the table to know)
- Cell junctions: tight, adherens, desmosomes, gap, hemidesmosomes
- Extracellular matrix: collagen types, elastin, ground substance
- Glomerulus and the filtration barrier: podocytes, mesangium, JGA
- Where blisters form: pemphigus vs pemphigoid
- Connective tissue proper: cells and fibres
Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice.
Sources: 4.2 Epithelial Tissue (OpenStax, 2022); Epithelial Tissue (National Cancer Institute, SEER Training Modules, 2024); 4.3 Connective Tissue Supports and Protects (OpenStax, 2022).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.