Three Types of Junctions n Occluding junctions Zonula

Three Types of Junctions n Occluding junctions – Zonula occludens n n n 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

Three Types of Junctions, cont’d n Anchoring Junctions (lateral face) n Zonula Adherens n n Lateral adhesion Continuous band of transmembrane cadherins bound to catenin/vinculin/actin on cytoplasmic side Adhesion is Ca+ dependent Macula Adherens (Desmosomes) n n n 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)

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

Basal Face n Basement Membrane n Basal lamina n n n n Cell-ECM junctions n n n 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 Focal Adhesions (via actin) Hemidesmosomes (present in mechanically abraded tissues) PM foldings

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