Epithelium Fall 2007 - 1

Epithelium

Surface Modifications,

Microvilli

Three Types of Junctions 

Occluding junctions – Zonula occludens 

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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 

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

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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)

Three Types of Junctions, cont’d  Communicating Junctions  

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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

Basal Face 

Basement Membrane 

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

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Cell-ECM junctions  

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Focal Adhesions (via actin) Hemidesmosomes (present in mechanically abraded tissues)

PM foldings

Glands Exocrine vs Endocrine – How are they different?

What are these?

Exocrine Glands  Merocrine 

Vesicle bound products; exocytosis

 Apocrine 

Released in apical portion of cell

 Holocrine 

Apoptosis related release (eg., sebaceous glands)