The polarity of ephitelial cell (apical x basolateral) is established by …
tight junctions
+
internal organization of organelles
The transport of substances through epithelial tissue is basic …
transcellular
(large molecules - through the cells)
paracellular
(between the cells)
How do tight junctions regulate the paracellular pathway?
keep basolateral and apical surface separate
→
formation of 2 distinct compartments (barrier)
How can we detect the lost of polarized organization of the epithelial tissue?
Antibodies against proteins specific for either the apical or basolateral membrane
→
useful to early index of neoplasticity
Epithelial Tissue generalities
avascular → interstitial fluid from connective tissue
proliferation → stem cells
hematoxylin-and-eosin staining
- (hematoxylin - blue + acid components/basophilic + DNA)
- (eosin - pink + basic components/acidophilics + proteins)
Epithelial Tissue
Simple Columnar Epithelium
intestine
(large and small)
Epithelial Tissue
Simple Squamous Epithelium
endothelium (blood vessels)
mesothelium (serous membranes)
epithelium (glomerular capsule)
Epithelial Tissue
Pseudostratified Columnar Epithelium
nasal cavity
trachea
bronchi
epididymis
Epithelial Tissue
Transitional Epithelium
Ureter
Bladder
Epithelial Tissue
Stratified Squamous Epithelium
skin (keratinizing)
oral cavity
pharynx
esophagus
Epithelial Tissue
Simple Cuboidal Epithelium
renal tube
salivary gland acini (secretory cells)
Epithelial Tissue
Stratified Cuboidal Epithelial
salivary gland (ducts)
Epithelial Tissue
Glands
Unicellular (GI and respiratory tract)
Multicellular (exocrine or endocrine)
- simple cuboidal epithelium mainly
- exocrine glands - ducts
Cytoskeletal Elements
Microfilaments = actin
- G-actin → globular monomer
- F-actin → 7 nm diameter helical filament (atp-polymerization)
- Filaments are constantly ongoing assembly and disassembly (tread milling)
- Polarity → barbed end (+) = polymerization // pointed end (-) = depolymarization
- Contractile + Motile (in addition to miosin)
- Important function in mitosis and meiosis (contractile ring)
Cytoeskeletal Elements
Intermediate Filaments
- 10 nm diameter filaments
- stable once form
- structural stability
- type I: keratin (in all epithelial cells)
- type II: desmin, vimentin, glial fibrillary acid protein, peripherin
- type III: neurofilaments
- type IV: lamins (3 types) - nuclear envelope
Cytoeskeletal Elements
Microtubule
- 25nm - diameter hollow tubes
- constantly ongoing assembly and disassembly
- “track” for intracellular transport → vesicles and molecules
- transport → ATPase motor molecules
- dynein - retrograde
- kynesin - anterograde
- true cilia + flagella + mitotic spindle
Cell Adhesion
Molecules
- Cadherin + Selectin
- calcium ion-dependent
- extracellular portion ⇔ another cell’s cadherin (dimer - trans biding)
- cytoplasmatic portion ⇔ actin filaments (catenin complex of proteins)
- Integrins
- calcium ion-independent
- extracellular domain ⇔ fibronectim + laminin
- cytoplasmatic domain ⇔ actin filaments
- component of hemidesmossomes
- interactions between leucocytes and endothelial cells
Cell Adhesion
Basement Membrane
- Basal Lamina
- type IV colagen
- gyicoproteins (eg. laminin)
- proteoglycans (eg. heparin sulfate)
- Reticular Lamina
- reticular fibers
Cell Junctions
Tight junction (zonula occludens)
- barrier to difusion → polarity
- punctate contact near the apical end
- occludens (ZO - 1,2,3) + claudin proteins
Cell Junctions
Adheren Junctions (zonula adherens)
- belt around the entire apicolateral circumference
- immediatly below zonula occludens
- cadherins spam (actin filament)
Cell Junctions
Desmossome (macula adherens)
- anchoring junctions
- extracellular → cadherins span
- intracellular → tonofilaments (large bundles of intermediate filaments)
Cell Junctions
Hemidesmossome
- adherence to basement membrane
- intracellular → intermediate filaments
- extracellular → integrins binds to fibronectin (fibronectin + laminin bind to collagen in the basement membrane)
- permeability + cell motility at embryogenisis + cell invasion (neoplasic)
Cell Junctions
Gap Junction
- communicating junctions
- passageway for ions and small molecules
- connexons → 6 connexin molecules
- not associated with cytoskeletal filament
Membrane Specialization
Microvilli
- contains actin
- increase contact surface (absortive)
- GI tract + respiratory tract (columnar epithelium) + proximal tubule (kidney)
- stereocilia → epididymis (long) + sensory cells in inner ear (short)
