Today: Epithelial Tissue

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Today Epithelial Tissue Modifications of
epithelium (Classification of epithelial
membranes) Epithelial Glands
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Stratified squamous (nonkeratinized)
epithelium -location, function Stratified
squamous (keratinized) epithelium -keratin in
cells -location, function
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Stratified Cuboidal Epithelium Stratified
Columnar Epithelium Transitional
Epithelium Pseudostratified Columnar
Epithelium -ciliated
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What epithelia have in common -polarity. The
luminal and serosal surfaces Apical and
basolateral surfaces -cell surface
specializations eg. -apical domain/basolateral
domain
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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.
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Glands Parenchyma - glands and ducts Stroma -
connective tissue (CT) supporting the parenchyma
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• Exocrine glands
• secretory portion and duct portion
• Endocrine glands

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Multicellular Exocrine Glands -Simple
tubular branched tubular coiled
tubular acinar branched acinar -Compound tu
bular acinar tubular acinar
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Know glands by the type of secretion -mucous -
serous -mixed glands -serous demilunes in
salivary glands
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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)
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Unicellular exocrine glands -goblet cells -
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Junctional Complex Terminal bars -Occluding
junctions -Adhering junctions
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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
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Adhering Junctions zonula adherens - encircle
cells macula adherens - desmosome - like spot
welds
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Zonula Adherens
-intercellular space is 15 - 20 nm This space
contains cadherins - calcium dependent transmembra
ne linker proteins. -on the intracellular side,
proteins, vinculin and a-actinin bind the mb to
actin web
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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
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Hemidesmosomes Anchor epithelial cells to the
basal lamina -attachment plaque with
desmoplakin -IF, keratin tonofilaments dont
enter the plaque -trans-membrane linker proteins
are integrins -these bind to laminin type IV
collagen of basal lamina
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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