Epithelium - Elul

Epithelium

Continuous sheet of adherent vascular cells, lines internal and external surfaces, comprises glads

Classify by layers

Simple - One layer
Stratified - Multiple layers

Classify by shape (simple)

Squamous - elongated//flattened - frictionless surface
Cuboidal - looks like a cube - kidney ->secretion and absorption
Columnar - nucleus basal - small intestine lining ->secretion, absorption, protection

Simple Cuboidal//Columnar

Secretion//absorption
Line kidney or GI
Mircovilli found of some apical surfaces to increase surface area, has sugar coating (called striated//brush border)

Classify by shape (stratified)

-Squamous - non/keratinized - outermost layer are squamous shaped. Skin is keratinized (thickness varied throughout body)
-Cuboidal//Columnar - (rare) - sweat and salivary glands. 2-3 layers

Transitional Epithelium

Found in the bladder, apical layer is dome shaped when relaxed, when bladder is full -> more squamous shaped

Pseudostratified Columnar Epithelium

All cells on basal surface, nuclei at different level, only some reach apical surface, Cillia on apical surface

**respiratory epithelium

Cilia

On apical surface of pseudostratified columnar respiratory epithelium, bendable, basal body 9 mt triplets with 9mt doublets surrounding central doublet forming "hairlike" projections

**stereocilia ->specialized form of microvilli

Cell Surface Modifications

Cell - Extracellular Junction
Cell - Cell intercellular junction

Hemidesmosomes

Cell-ECM
-Attach epithelial cells to ECM
-Integrins through adaptor proteins link intermediate filaments to collagen (ecm)

**Epidermolysis Bullosa->mutation of hemidesmosome components leads to separation of epidermis/dermis border -> results in blistering

Tight Junction

Cell-Cell
Proteins occludins and claudins
Substances cant travel between cells
divide cells into apical and basal domains

Zonal Adherens

Cell-Cell
Contains cadherin and connects to actin

**cadherin = transmembrane homophillic binding protein

Desmosomes

Cell-Cell
Contains cadherin and plaque proteins and connects to intermediate filaments

Cell-ECM and Cell-Cell Junctions and cancer cell metastasis

Cancer cells have decreased expression of cell-cell junction proteins (cadherin) and increased expression of cell-ECM junction proteins(integrins) -> can physically detach from neighbor and travel, and can attach to new place w/ integrins

Simple Cuboidal

Simple Columnar

Simple Squamous

Stratified Squamous Non-keratinized

Stratified Squamous keratinized

Pseudostratified Columnar

Stratified Cuboidal/Columnar

Transitional Epithelium

Cell-Cell Junctions