Epithelium 3

Cell polarity

Structural and functional differences between distinct regions of an epithelial cell

Apical domain

directed towards exterior surface, lumen of cavity, or free space

specializations such as: microvilli, stereocilia and cilia

Lateral domain

contacts neighboring cells and contains cell junctions that provide adhesion and communication

Basal domain

faces and attaches to the basement membrane anchoring the epithelium to underlying connective tissue

Junctional complexes

The point at which epithelial cells join to one another and establishes polarity

regulates paracellular movement of ions and water both directions

Microvilli histology

demonstrates eosinphilic brush border

DO NOT resolve well at light microscope level

Microvilli function

increase apical surface area

numerous transport protein are embedded along the microvilli

Microvilli location

prevalent in small intestine and kidney epithelium

Stereocilia histology

very long immotile processes

resemble hairs of a paint brush

stair case pattern with non uniform lenght

Stereocilia function and location

increases surface area for absorption and secretion in epididymis and ductus deferens

sensory mechanoreceptor that detects vibration in inner ear

Cilia histology

visible uniform hair-like projections

Cilia function

motile cilia contain a microtubule core that contain molecular motor protein that uses ATP that creates a synchronized beating pattern that moves fluid

Cilia location

Oviduct

Respiratory duct

Cell adhesion molecules (CAMs)

links plasma membrane of adjacent epithelial cells togehter

Occulding junctions

forms primary paracellular diffusion barrierand maintains cellular polarity through belt like zipper junctions

Occludin

maintains cellular polarity by restricting movement of lipids and proteins between apical and lateral domains

Claudin

forms channels for paracellular transport of ions, small molecules and water

determines leakiness of junction

Anchoring junctions

provide mechanical stability by linking cytoskeletons of adjacent

linked to actin cytoskeleton to resist seperation of adjacent cells

Cadherin

regulate cell adhesion through interaction on adjacent cell

Catenin

links cadherin to actin cytoskeleton

Cadherin-catenin complex

regulates differentiation, migration, and proliferation

major tumor suppressor

Communicating junctions

provide direct communication between adjacent cells

Desmosomes primary function

mechanical adhesion cell to cell that spreads out force across the tissue

spot weld

Desmosomes histology

can be observed as spin projections in stratum spinosum from artifactual separation

Gap junctions

Permit direct passage of signaling molecules

number of GAP junctions varies widely across epithelia, smooth and cardiac muscle, and neurons

Basal domain components

Basement membrane and ECM junctions

Basement membranes

structure located next to basal domain of epithelia and connective tissue

ECM juctions

anchor cell to ECM

focal adhesions and hemidesmosomes

Basement membrane staining

only visible with PAS stain or silver stain

Basement cell proteins

type IV collagen: forms scaffold

Laminins: provide binding site for integrins

Proteoglyans: regulates passage of ions

Reticular fibers: reacts with PAS and silver stain

basement membrane functions

anchors epithelia to CT

Seperates different cell types

Regulates movement of substances

guide for wound healing and regeneration

regulates cellular signaling

Focal adhesions

link actin cytoskeleton to ECM

transient attachment

facilitate cellular migration during wound repair

Hemidesmosomes

Localised adhesion of epithelium to BM

Stable attachment

provide attachment from epithelial cell to underlying CT