BIOL 3100 Lecture Notes - Lecture 16: Choroid Plexus, Tight Junction, Paracellular Transport
19 Oct 2019
School
Department
Course
Professor
Intercellular connections
• Cells attach to each other & to surrounding EC matrix, forming functional unit
• Present in other tissues, but prominent in epithelia
• Different types of attachment serve different purposes:
a. Occluding junctions form permeability barrier (zonula occludens or tight junctions)
b. Anchoring junctions: providing mechanical strength ( zonula adherens, desmosomes,
hemidesmosomes)
c. Communicating junctions permit ionic/molecular movement b/t adjacent cells (gap
junctions)
• Seen together forming junctional complexes
Junctional Complexes of Epithelial cells
• Desmosomes
• Gap junctions
• Tight junctions
• Adhering junctions
Anchoring cells to Each other
• Provide mechanical strength & stability; ability to withstand shear forces
• Anchor cytoskeleton of adjacent cells
• Include zonula adherens, macular adherens (desmosomes)
Basic structure
• Integral transmembrane linker glycoproteins
• Cytoskeletal filaments
• Intracellular attachment proteins
Functional Implication of Tight Junctins
• Prevents/control paracellular molecular movement
• Used to create functional tissue compartments
• Prevents back-diffusion of actively transported molecules
• Functions to limit movement of membrane proteins
• Absorption: transport from lumen to blood vessels
• Secretion: blood vessel to lumen (eg. Choroid plexus & sweat gland)
Gap Junctions - Communicating Junctions
• Channels formed by adjacent connexons
• Each Connexons composed of 6 proteins subunits called connexins that span lipid bilayer
• At junction, membranes seperated by gap of 2nm
• Connexon open/close with conformation change.
• Provides cytoplasmic continuity b/t adjacent cells
• Permits passage of ions & small molecues
