The reasoning: structure of contact → function of tissue
| Junction | Molecules | Function | Disease link |
|---|---|---|---|
| Tight (zonula occludens) | claudins, occludin, ZO‑1 | paracellular barrier ("gate") and membrane polarity ("fence") | claudin‑16/19 → familial hypomagnesaemia–hypercalciuria |
| Adherens (zonula adherens) | E‑cadherin (Ca²⁺‑dependent) → catenins → actin | belt adhesion, tissue organisation | CDH1 loss → diffuse gastric and lobular breast cancer |
| Desmosome (macula adherens) | desmogleins/desmocollins → plakoglobin → keratin | strong spot adhesion | pemphigus vulgaris (Dsg3 ± Dsg1) — intraepidermal, Nikolsky positive |
| Hemidesmosome | integrin α6β4, BP180 (collagen XVII), BP230 | anchors basal cells to basement membrane | bullous pemphigoid — subepidermal, tense bullae |
| Gap junction | connexons (6 connexins) | electrical and metabolic coupling | GJB2 (Cx26) commonest genetic deafness; Cx32 → X‑linked CMT |