1. Three Types of Junctions
Occluding junctions – Zonula occludens
restrict and direct movement of fluids in intercellular space
Focal adhesions in a band around cell; composed of
Transmembrane = occludin,
cytoplasmic proteins = ZO 1-3 (1 is tumor supressor, 2 is part of EGF signaling, 3 is linker)
Breach ZO – leaky epithelia
Most apical attachment, restricting movements of PM proteins and maintaining integrity of apical vs. basal/lateral surfaces
Tightness of anastomosing network differs b/w tissues

2. Three Types of Junctions, cont’d
Anchoring Junctions (lateral face)
Zonula Adherens
Lateral adhesion
Continuous band of transmembrane cadherins bound to catenin/vinculin/actin on cytoplasmic side
Adhesion is Ca+ dependent
Macula Adherens (Desmosomes)
High tensile strength
Desmoplakin/plakoglobin attach to intermediate filaments
Not a continuous structure around cell
Attachment plaque – shock absorber
Attach to other cells by desmogleins (cadherin zipper)

3. Three Types of Junctions, cont’d
Communicating Junctions
Gap junctions
Lateral pores composed of connexins
Pore size alters, but still restricts cell-cell communication physically
Lowers electrical resistance in cells (permits ion passage)
Protein = Connexin

4. Basal Face Basement Membrane Cell-ECM junctions PM foldings
Basal lamina
Collagen
Proteoglycans
Laminin
Entactin and Fibronectin
H & E stains poorly; use PAS
Beneath Basal Lamina is Reticular lamin (connective tissue)
Attachment, Compartmentalization, Filtration, Polarity induction, Tissue scaffolding
Cell-ECM junctions
Focal Adhesions (via actin)
Hemidesmosomes (present in mechanically abraded tissues)
PM foldings

5. Exocrine Glands Merocrine Apocrine Holocrine
Vesicle bound products; exocytosis
Apocrine
Released in apical portion of cell
Holocrine
Apoptosis related release (eg., sebaceous glands)