What is Cell Junction or Intercellular Bridge?
The point of contact between adjacent plasma
membranes is called cell junction or intercellular bridges.
Cell junctions are cellular structures
consisting of multi-protein complexes. It is intercellular connections between
the adjacent cells of plasma membranes of animal tissues.
It provides contact or adhesion between neighbouring
cells or between a cell and the extracellular matrix in animal tissues.
Cell junctions are especially found in huge
amounts in epithelial tissues. It also maintains the paracellular barrier of epithelium
and control paracellular transport.
Check out here what is epithelial
tissue? What are the types and functions of epithelial tissue?
Cell junctions help to hold animal cells
together. It is combined with cell adhesion molecules and the extracellular matrix.
Cell junctions are important in reducing the stress placed upon cells.
Types of Cell Junction
There are three major types of cell
junction-
1. Tight Junction or Occluding junction or Zonula occludens
2. Anchoring junction or Zonula adherens
a. Desmosomes (macula
adherens)
b. Hemidesmosomes
c. Adherens junction
3. Gap Junction or Communicating junction
1. Tight Junction
Tight junction binds cells together and
form a fluid-tight seal between the cells. The purpose of tight
junctions is to keep liquid from escaping or leaking between cells. it is allowing
a layer of cells to act as an impermeable barrier.
For example,
In the kidney, act as a barrier.
The tight junctions between the epithelial
cells lining of the bladder prevent urine from leaking out into the extracellular
space.
2. Anchoring junction
Anchoring junctions are cell junctions of
protein complexes that mediate the anchored (adhesion) of cells to other
cells or to the extracellular matrix.
Cells within tissues and organs must be
adhesion to one another and attached to components of the extracellular matrix.
It plays an important role in keeping the cells together and the structural
cohesion of tissues.
They are commonly found in tissues that are
prone to get mechanical stress.
For
example; skin and heart
Types of Anchoring Junctions
There are three types of anchoring
junctions-
1. Desmosomes
2. Hemidesmosomes, and
3. Adherens junctions
Desmosomes
Desmosomes are stronger connections that
join the intermediate filaments of neighbouring cells. This cell
structure is specialized for cell-to-cell adhesion.
Both desmosomes and hemidesmosomes join the
intermediate filaments of neighbouring cells.
Hemidesmosomes
This
structure facilitates the stable adhesion of basal epithelial cells to the
underlying basement membrane.
Adherens junctions
Adherens junctions join the actin filaments
of neighbouring cells together.
For example; epithelial
and endothelial tissues.
Adherens junctions play an important role
in linking cells to another cell or to the extracellular matrix.
3. Gap Junctions
Gap junction is also called Communicating junctions, is
a specialized protein complexes channels
between neighbouring cells that allow for the transport or flow of ions, water,
and other substances. It also allows electrical and chemical signals to pass
from cell to cell.
For example; between
cardiac muscle cells in the heart.
Gap junctions Function
1. Gap junctions are especially important in enabling communication
between neighbouring cells via specialized protein complexes.
2. Gap junctions allow
direct chemical communication between adjacent cellular cytoplasm through
diffusion without contact with the extracellular fluid.
3. Gap junctions play a vital role in the uniform contractile of the heart muscle, relevant in signal
transfers in the brain. Their absence shows a decreased cell density in the
brain.
4. Gap junctions are
also important for retinal cells and skin cells in cell differentiation and cell
proliferation.
Know here types of
tissues and embryonic
origin of tissues.
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