Cell Junctions

  • Created by: Huzaima1
  • Created on: 03-01-19 14:23

Tight Junctions and Gap Junctions

  • Tight junctions prevent movement of substances
  • Formed by the fusion of integral proteins of adjacent cells
  • prevent anything passing through the extra cellular space between them. E.g. cells lining the digestive tract.
  • Tight junctions bar the movement of dissolved materials through the space between epithelial cells.
  • There is no intercellular space where there is a tight junction.
  • Long rows of tight junction proteins form a complex meshwork seen at the bottom of the freeze etched image
  • Gap junctions allow movement of substances
  • The adjacent cells are connected by hollow cylinders called connexons made of trans membrane proteins. Found in electrically excitable tissues for synchronization  e.g. heart and smooth muscle
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Adherens junctions, Desmosomes and Hemidesmosomes:

Desmosomes and Hemidesmosomes:

  • These are anchoring junctions held together by linker protein filaments called cadherins or integrins extending from button like thickenings called plaques.
  • Distributes tension and prevents tearing.
  • e.g. skin and heart muscle

Adherens Junctions

  • Plaque which attaches to membrane proteins and the microfilaments of the cytoskeleton
  • Often form adhesion belts.
  • Resist separation in contractile activities such as peristalsis
  • Adhering junctions maintain cellular position
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Cell to Cell junction examples

  • Mechanical coupling:
  • There is a small gap (0.02 mm) between the membranes of adjacent cells which is filled with connective tissue.
  • This firmly binds two adjacent cells together
  • Cells are bound together more strongly at certain points called desmosomes.
  • Electrical coupling:
  • The longitudinal segments contain specialised regions where the membrane of the adjacent cells come very close together.
  • In the nexus (gap junction) regular arrays of proteins called connexinsare found
  • These form large channels which allow the passage of ions and other small molecules between one cell and another. 
  • Intercalated discs have two important roles
  • They act to firmly bind adjacent cells together (mechanical coupling) but also to allow electrical coupling between adjacent cells
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