Expansion
Tight junctions seal, adherens and desmosomes anchor, gap junctions communicate
Expansion
In order from apical to basal in an epithelial cell:
- Tight junction (zonula occludens): seals the paracellular space, creating a permeability barrier and maintaining apical-basal polarity. Claudins and occludins. Forms the blood-brain, blood-testis and blood-thymus barriers
- Adherens junction (zonula adherens): anchors via E-cadherin to the actin cytoskeleton
- Desmosome (macula adherens): spot welds via desmoglein, anchoring to intermediate filaments (keratin). Provides mechanical strength
- Gap junction: connexons allowing direct passage of ions and small molecules, giving electrical and metabolic coupling
- Hemidesmosome: anchors the cell to the basement membrane via integrins
Disease maps onto each:
- Pemphigus vulgaris: antibodies to desmoglein, so cells separate within the epidermis giving flaccid intraepidermal blisters and a positive Nikolsky sign
- Bullous pemphigoid: antibodies to hemidesmosomes, giving tense subepidermal blisters
- Loss of E-cadherin permits invasion and metastasis, and characterises diffuse gastric and lobular breast carcinoma
- Gap junctions coordinate cardiac and smooth muscle contraction