Epithelium 4 Flashcards
(27 cards)
Intercellular junctions types:
- Tight or occluding junctions
- Anchoring junctions
- Gap junctions
- Desmosores (macula adherens)
Tight a occluding junctions structure
(Like a glue )
Adjacent cell membranes appear used together due to tight interactions between the transmembrane proteins
* cluadin and occluding
Function at occluding junctions
- Molecules only go through the cells when crossing the epithelium ( transcellular pathway rather than the para cellular pathway)
- Prevents passive flow of materials between the cells
- Maintain 2 distinct membrane domains topical and basolateral )
Site of occluding junctions,
Present at the apical end of cells
Encircling the cells ( zonulae occludes )
Anchoring junctions: zonulae adherent
( touching finger tips )
Structure
- Cell adhesions are mediated by cadherins transmembrane proteins
- identical cadherins bind to each other from adjacent cells
*At the cytoplasmic ends cadherins bind to catching that link to actin - a small electron dense plaque appears at the intercellular component. (Where fingers touch)
Function of anchoring junctions
1.tight and adherent junctions hold cells together
2. Stabilize, and strengthen the occluding bands
.desmosome structure
Disc shaped structures that consists of a cytoplasmic adhesions plaques formed of proteins and placed on the cytosolic race of the 2 cell membranes
The 2 plaques are connected by transmembrane linker proteins which extend into the intercellular space terming an interlacing network which binds to the cells and appears as a dense line in the intercellular space
Gap junction structure
Pores/tunnel between cells
They consist of aggregated transmembrane protein complexes that form from circular patches in the plasma membrane
Form hexameric complexes called connexons
Each connexon has a central hydrophilic pore
Function of gap junctions
- Permit intercellular exchange of small molecules
*Provides synchronous contractions in cardiac muscle cells
Strongest junction?
Desmosomes due to intermediate filaments
Interdigitations: function, and site
- Site: kidney tubules
- function: provide a wide surface fer intercellular passage of material
Intercellular canaliculi: function and site
(secretary material mom adjacent cells is accumulated in channels)
- Function: carry the secretions to ducts
*Site: liver cells
Modification of the PM at the apical parts
- Cilia
- Stereocillia
- Microvilli
- Cuticle
- Caveoles
Microvili structure
Projected in the lumen
Smaller than cilia.
Has a thick glycocalyx ( cell coat ) that contains enzymes
Contain bundled actin microfilaments
Microvili function and site
Function:Increase apical surface area for better absorption
Site: intestines
Cilia structure
*Highly motile apical structures
*Contain internal arrays of microtubles
*each microtubule has a core structure of 2 central microtubules surrounded by 9 peripheral microtubules (axoneme)
*the peripheral ones are attached to the centrals by radial spokes (dynein)
*the basal body anchors the axoneme
*the basal body has triplets of microtubules and protofilaments anchoring the structure
Function of cilia
For transportation due to rapid beating patterns that move fluid in one direction along the epithelium
Primary cilium (does NOT move) enriched with receptors to detect stimuli
Site of cilia
Respiratory tract
Cuticle structure
Rich in proteins on the outer lamina of the plasma membrane
Function of cuticle
On the epical surface for protection
Site of cuticle
Ureter
Urinary bladder
Claveolae structure
The secretory surface of cells have invaginations (caves) which result from exocytosis and pinocytosis
Sites of caveolae
Endothelial lining of blood capillaries
Modification of the PM at the cell base types
1.basal infolding
2.hemidesmosomes
