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Epithelium
Derivatives from the
three germ layers
- Endoderm: skin, CNS and PNS, neural crest cells, eyes, internal
ears
- Mesoderm: bones, ct, urogenital, CVS
- Ectoderm: gut and gut derivatives
- Just remember this; extra: ectoderm → skin epidermis, sweat
glands, duct oral surface, vagina, anus
Common properties
of epithelial cells
1. All with junctional structures (desmosome, hemidesmosome)
2. All rest on basement membrane
3. Cytokeratin as intermediate filament
4. Avascular
Composition of
basement
membrane
- Basal lamina + protein layer + lamina recularis
Basal lamina
- Lamina lucida (cell membrane) + lamina densa (collagen IV)
How do cancer cells
invade tissues
- Basement membrane contains collagen IV (lamina densa) →
cancer cells secrete type IV colleganase → invasion
Protein layer
- Collagen VII + fibrilla
Lamina reticularis
- Collagen III
Summary of
collagen types
present in
basement
membrane
- IV (from epithelium)
- VII (protein layer)
- III (from ct)
Function of
cytokeratin
- Cell adhesion via desmosome and hemidesmosome
- Tumour marker
Replacement by
stem cells
- Intestinal epithelium: base of crypts
- Skin epithelium: stratum basale
Metaplasia
- Faced with a chronic change in environment → change from
one type to another e.g. smoking causes squamous metaplasia
in respiratory epithelium
