epithelial tissue and its variations - univerzita karlovavyuka-data.lf3.cuni.cz/cvse1m0001/141...
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Epithelial tissue and its variations
141
Definition Avascular tissue Cells are closely apposed and adhere to
each other by cell junctions They exhibit functional and
morphological polarity They are attached to basal lamina
Classification according to function
Covering and lining epithelial tissue– Protection– Absorption– Transportation
Secretory – glandsReceptor – sensory organs Contractile (myoepithelial cells)
Cell polarityApical domainLateral domainBasal domain
Functionally different = specialized surfaces
Cell junctions divide cell membrane into apical and basolateral region
The apical domain modifications
Microvilli – frequent in all cell types – sign of absorption – brush border (striated border)
Stereocilia – – Male genital system – extremely long
and branching microvilli– Sensory hair cells – derived from
microvilli - mechanoreceptorsCilia – motile cilia, primary cilia (sensoric),
nodal cilia
MicrovilliActin filaments 20-30 –
anchored to membrane by villin
Crosslink by actin bundling proteins
Terminal web – actin, spectrin, myosin II
Brush border
Enlargement of apical domain
Enzymes, carrier proteins, ion channels
Glycocalyx
Occurence : enterocyte, cells of proximal tubule in kidney
Stereocilia
Extremely long microvilli – resorption – actin,
α actinin instead of villin
Stereocilia in sensory hair cells of inner ear
Mechanoreceptors – actin and espin crosslink
Structure is similar to microvilli
Cilia
Kinocilia and flagella – axonema – 9+2 microtubules + dynein
Primary cilia – immobile – lack of motor-proteins.
• Sensoric function – chemoreceptor, osmoreceptor, mechanoreceptor
• Primary cilia of developing cells are essential for normal morphogenesis
Nodal cilia – bilaminar embryonic disc – primitive node - similar to primary cilia but wit ability of rotational movement
KinociliaLength 5-10μm Axonema: 9 duplets A13,
B10 + 2 central microtubules
Basal body = centriol – 9 triplets
Basal foot and striated rootlet – coordination of ciliary movement and anchorage to cytoplasm
Primary cilia9+0Lack of motor-
proteinand central pair of
microtubulesBasal body Primary cilia
formation is synchronized with cell cycle progression and centrosome duplication events
Receptor:Rods and conesHair cells of inner earOlphactory
epitheliumlMechanoreceptor – in
ducts of glands – control of Ca++ in cell – polycystic kidney disease, retinitis pigmentosa
Nodal cilia
9+0, but motile!!!Rotational
movementMechanim
generating the right-left asymetry
Lateral domain modification
• Junctional complex:• zonulae occludentes
– tight junctions• zonulae adherentes• maculae adherentes
(desmosomes)• gap junctions• Lateral infoldings
(plicae), interdigitations
Intercellular cohesiveness is established by cell-to-cell adhesive molecules
• CAM – cell adhesion molecule• Cadherins - transmembrous proteins
(intracellular domain is bound to the cytoskeleton, actinu/intermediate filaments, extracellular domain fills up the intercellular space)
• Disorder: lost of cohesiveness – invasiveness of tumor cells
Zonula occludens – tight junction
Apical region of the junclional complex
Diffusion barrier Separation of apical
and lateral domains
Occludins and claudins
-anastomosing belts - actin
Anchoring (adhesive) junctions - zonula adherens
E-cadherin, Catenin, vinculin +
α-actininActin
Ca++ dependent
Anchorin junctions- desmosome
Desmocollins and desmogleins
Intermediate filaments (cytokeratins)
Ca++ dependent
Communicationg junctions – gap junction (nexus)
Accumulation of transmembrane channels or pores – connexons – inchange of molecules between cells - signaling
Basal domain – basal labyrint
Enlargement of basal surface + mitochondria
= Absorption of ions – Na/K ATPase and sodium pump
Occurence – proximal and distal tubules of kidney
Basal domainAttachment to the
extracellar matrix (focal adhesions – FAK and hemidesmosomes) - integrins
Focal adhesion – actin
Hemidesmosome - cytokeratin
Basement membrane (LM) is the layer of extracellular material separating epithelia from the
connective tissue• Basal lamina and lamina reticularis • Basal lamina (EM): lamina densa and lamina
rara • Lamina rara: receptors for laminin and
fibronectin • Lamina densa : laminin + collagen IV,
proteoglycans and glycoproteins• Lamina reticularis: reticular fibres (collagen III),
anchoring fibrils (collagen VII), fibrilin
Epithelial tissueCovering – cells are
polarized with free surface
Forming cords- no free surface – endocrine glands
Reticular – epitheloreticular cells - network - thymus
Secretory portion = parenchyma
Classification of epithelial tissue (covering)
SimpleSquamousCuboidalColumnarPseudostratified
columnar
Classification of epithelial tissue (covering)
StratifiedSquamous
• Keratinized• Nonkeratinized
CuboidalColumnarTransitional (Urothelium) -
Glands
Exocrine glands – secrete their product onto a surface
Secretory portion and duct – cells have a free surface
Endocrine – secrete their product (hormones) into the blood Cells with free
surface – thyroid gland
Cords of cells