• 180 likes • 201 Views
Explore the classification of epithelial membranes, functions of epithelial glands, and detailed insights into different epithelial tissues. Learn about junctional complexes and the types of glands based on secretion and release mechanisms.
E N D
Today: Epithelial Tissue Modifications of epithelium (Classification of epithelial membranes) Epithelial Glands
Stratified squamous (nonkeratinized) epithelium -location, function Stratified squamous (keratinized) epithelium -keratin in cells -location, function
Stratified Cuboidal Epithelium Stratified Columnar Epithelium Transitional Epithelium Pseudostratified Columnar Epithelium -ciliated
What epithelia have in common: -polarity. The luminal and serosal surfaces Apical and basolateral surfaces -cell surface specializations eg. -apical domain/basolateral domain
Some epithelial cells have: Microvilli -striated border, brush border, stereocillia -actin filaments cross linked and attached to apex by villin -terminal web has actin, spectrin, and intermediate filaments.
Glands: Parenchyma - glands and ducts Stroma - connective tissue (CT) supporting the parenchyma
Exocrine glands • secretory portion and duct portion • Endocrine glands
Multicellular Exocrine Glands -Simple *tubular *branched tubular *coiled tubular *acinar *branched acinar -Compound *tubular *acinar *tubular acinar
Know glands by the type of secretion: -mucous -serous -mixed glands -serous demilunes in salivary glands
Know glands by the way the secretion is released: -Merocrine, by conventional exocytosis -Apocrine, a portion of the cell breaks off (lactation) -Holocrine, entire cell is released (sebaceous gland)
Unicellular exocrine glands -goblet cells -
Junctional Complex: Terminal bars -Occluding junctions -Adhering junctions
Occluding Junction: -aka zonua occludens, tight junction -transmembrane junctional proteins, like a zipper -leakiness of the junction depends on the number of zipper rows -the branching rows of transmembrane junctional proteins can be seen by freeze fracture TEM -membrane is pentalamellar by thin section TEM
Adhering Junctions: zonula adherens - encircle cells macula adherens - desmosome - like spot welds
Zonula Adherens: -intercellular space is 15 - 20 nm This space contains cadherins - calcium dependent transmembrane linker proteins. -on the intracellular side, proteins, vinculin and a-actinin bind the mb to actin web
Macula adherens (desmosome): -intercellular space is 30 nm -attachment plaque on the intracellular side of the mb made of desmoplakin. -cytokeratin (intermediate filaments, 10 nm) attach to the plaque. -intercellular space has desmoglein and cadherins
Hemidesmosomes: Anchor epithelial cells to the basal lamina -attachment plaque with desmoplakin -IF, keratin tonofilaments don’t enter the plaque -trans-membrane linker proteins are integrins -these bind to laminin & type IV collagen of basal lamina
Gap Junctions are communicating junctions -intercellular space is 2 - 3 nm -adjoining windows between cells -windows are connexons, made of protein connexin -gap junctions pass ions, small molecules (cAMP) -opening and closing of the gaps can be regulated