Epithelia Flashcards
Key functions of epithelia
Selective barriers
Secretory
Protection
Cell junctions
Tight junction Desmosome Hemidesmosome Adherens junction Gap junction
What are intermediate filaments made of
Keratin
What are microfilaments made of
Actin
Function of cytoskeleton
Strength, alter cell shape; link cytoplasm to membrane; tie cells together; muscle contraction
Features of tight junctions
Transmembrane sealing strands
Claudins and occludins key proteins
Join to actin and bind cytoskeletons of adjacent cells together
Electrically tight
Features of adherens junctions
More basal than tight junctions
Plaque layer of proteins on inside of cell
Cadherins span gap
Cadherins linked to actin by catenins
Function of adherens junction
Prevent separation of cells during contraction
Where do desmosome junctions occur
Lateral walls
Function of desmosomes
Resist shearing forces
e.g in cardiac muscle and epidermis
Features of desmosomes
Cadherins span gap
Cadherins attach to keratin which stretches across cell to desmosome on other side
Function of gap junctions
Direct connection between cells
Allow diffusion of material (1kDa)
Allow electrical signalling
Features of gap junctions
6 connexin proteins form a connexon/hemichannel
2 connexons form a gap junction
Function of hemidesmosome
Anchor basal surface to basement membrane
Features of hemidesmosomes
Integrin as transmembrane protein
Attaches to keratin in the cytoplasm and laminin in the basement membrane
Two structures of the basement membrane
Basal lamina
Reticular lamina
Formation and contents of basal lamina
Secreted by epithelial cells Laminins Collagen Proteoglycans Glycoproteins
Formation and contents of reticular lamina
Secreted by firoblasts
Fibrous proteins e.g fibronectin and collagen