WHAT ARE THE JOINTS / Junctions BY WHICH CELLS COMMUNICATE ?, ADD NOTES ON THEIR IMPORTANCE IN PHYSIOLOGIC FUNCTION

 


SUBJECT: PHYSIOLOGY

TOPIC: CELL PHYSIOLOGY

WRITER: GOGO ANDREW MNGUTSWENGA ‘amblo


QUESTION 29

WHAT ARE THE JOINTS BY WHICH CELLS COMMUNICATE ?, ADD NOTES ON THEIR IMPORTANCE IN PHYSIOLOGIC FUNCTION


Cell junctions are cell complexes found in cells that help to anchor cell to cell and cell to matrix. They are multi protein complex. They guard spaces within and outside the cell.

 They are found in all cells but most abundant in epithelial cells.


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TYPES

OCCLUDING JUNCTION (ZONA OCCLUDENS)

They are exclusively occlusive (sealed). They seal to prevent leakages. Substances pass only at the will of cells. The major protein that forms this junction is the claudins, although occluding also contribute, but their function isn’t known.

 Zona occludins are also associated with junctions. They are found in the gastrointestinal tract, wall of renal tubules and choroid plexus.


FUNCTION OF OCCLUDING JUNCTION

  • They provide semi-permeable barrier to substances with different chemical composition to the plasma membrane.
  • They are formed to seal between neighbouring cells
  • They also regulate cell polarity
  • They provide strength and stability to tissue.


WHAT ARE THE JOINTS BY WHICH CELLS COMMUNICATE ?, ADD NOTES ON THEIR IMPORTANCE IN PHYSIOLOGIC FUNCTION


ANCHORING JUNCTION

  • They hold walls together and also matrix. They are mechanical. They are found in areas that are subjected to mechanical stress, E.G; heart, muscle, epidermis. There are two classes of proteins here
  • Intracellular anchor protein, which form a plaque for the attachment of actin filament (intermediate filament).
  • Transmembrane protein: with one end attached to intracellular anchor protein and the other end to extracellular matrix.

TYPES

Desmosomes : hold cell to cell and belong to the family of cadherens

Hemidesmosomes : hold cells to extracellular matrix and belong to the family integrns

Zonula adherens : they are just below the tight junctions, encircling each of the interacting cels in a sheet. They belong to the family of bth cadherins and integrins.


Adherins and focal adhesion provide attachment for actin filament, this junction also contain intracellular signaling protein to signal the interior of the cell.


 Adherens and desmosomes hold cells together and belong to the family of cadherin protein. Focal adherens and hemidesmosome hold cells to extracellular matrix and belong to the integrins.


GAP JUNCTION

They are communication junction. Allows the exchange of substances and signals from the cytoplasm of one cell to another, the gap is about 2 – 4 nanometer.

 The potein here is the connexins. Connexin form channels called connexon. 4 – 6 connexin form a connexon. The connexon are transmembrane (integral protein).

 Connexon of some type are homometric, connexon of different type are heterometric.


FUNCTION OF GAP JUNCTION

Help in the propagation of action potential from cell to cell

Help in the transportation and exchange of material from one cell to another.


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