1. Some of the pictures presented in this lecture are taken from
12/6/2018

2. Facebook: amjadshatarat
Facebook: amjadshatarat
12/6/2018

3. Polarity
12/6/2018

4. 12/6/2018

5. 1-The lateral domain
12/6/2018

6. How the epithelial cells are attached to each other
What are these structures?
How the epithelial cells are attached to each other
What do you think?
12/6/2018

7. How the epithelial cells are attached to each other???
The lateral domain
What are these structures?
is characterized by the presence of unique proteins TO FORM junctional specializations
How the epithelial cells are attached to each other???
Before the advent of EM, the close apposition of epithelial cells was attributed to the presence of a viscous adhesive substance referred to as
intercellular cement
12/6/2018

8. Because of its location in the terminal or apical portion of the cell and its bar like configuration, the stainable material visible in light microscopy was called
The terminal bar
12/6/2018

9. a junctional complex The terminal bars
Electron microscopy has shown that the terminal bars
are specialized site that joins epithelial cells
The specific structural components that makeup the terminal bars are readily identified with the EM and are collectively referred to as
a junctional complex
These complexes are responsible for joining individual cells together.
There are three types of junctional complexes
1-Occluding junctions also called tight junctions
2-Adherens Junctions
3-Desmosomes
12/6/2018

10. 12/6/2018

11. below adherens junction?
Notice their positions
Are they above or
below adherens junction?
Tight Junctions
Tight Junctions
adherens junction?
adherens junction?
Desmosomes
12/6/2018

12. How about attachment as a function??!!!
1-Occluding junctions also called tight junctions, are impermeable and allow epithelial cells to function as a barrier., occluding junctions form the primary intercellular diffusion barrier between adjacent cells.
Function: by limiting the movement of water and other molecules through the intercellular space, they maintain physico-chemical separation of tissue compartments.
Because they are located at the most apical point between adjoining epithelial cells, occluding junctions prevent the migration of lipids and specialized membrane proteins between the apical and lateral surfaces, thus maintaining the integrity of these two domains
How about attachment as a function??!!!
12/6/2018

13. Where do you expect to find them?
Tight Junctions
consist of web like strands of transmembrane proteins that fuse together the outer surfaces of adjacent plasma membranes to seal off passage ways between adjacent cells
Where do you expect to find them?
1-the stomach
2-intestines
3-urinary bladder
and why?
They inhibit the passage of substances between cells and prevent the contents of these organs from leaking into the blood or surrounding tissues
Tight Junctions
12/6/2018

14. Read only
12/6/2018

15. Read only
12/6/2018

16. If this is true, then we have just created a barrier
How the nutrients would pass this barrier ?
12/6/2018

17. 12/6/2018

18. Read only
12/6/2018

19. 12/6/2018

20. 2-Adherens Junctions
contain plaque, a dense layer of proteins on the inside of the plasma membrane that attaches both to membrane proteins and to microfilaments of the cytoskeleton. Transmembrane glycoproteins called cadherins join the cells.
Each cadherin inserts into the plaque from the opposite side of the plasma membrane, partially crosses the intercellular space
(the space between the cells), and connects to cadherins of an adjacent cell.
Function: adherens junctions help epithelial surfaces resist separation during various contractile activities, as when food moves through the intestines
12/6/2018

21. In epithelial cells, adherens junctions often form extensive zones called adhesion belts because they encircle the cell similar to the way a belt encircles your waist.
Tight Junctions
Tight Junctions
adherens junction?
adherens junction?
12/6/2018

22. Read only
12/6/2018

23. 3-Desmosomes
Like adherens junctions, desmosomes contain plaque and have transmembrane glycoproteins (cadherins) that extend into the intercellular space between adjacent cell membranes and attach cells to one another
However, unlike adherens junctions, the plaque of desmosomes
does not attach to microfilaments.
Instead,
a desmosome plaque
attaches to elements of the cytoskeleton known as intermediate
filaments, which consist of the protein keratin.
The intermediate filaments
extend from desmosomes on one side of the cell across
the cytosol to desmosomes on the opposite side of the cell
12/6/2018

24. Read only
12/6/2018

25. Desmosomes junctions are common among the cells that make up
A-The epidermis (the outermost layer of the skin)
Desmosomes prevent
epidermal cells from separating under tension
B-cardiac muscle cells
from pulling apart during contraction
12/6/2018

26. At gap junctions, membrane proteins called connexins form tiny
fluid-filled tunnels called connexons that connect neighboring
cells Through the connexons, ions and small molecules can diffuse from the cytosol of one cell to another
Gap junctions
allow the
cells in a tissue to communicate with one another.
Gap junctions also enable nerve or muscle impulses to spread rapidly
12/6/2018

27. Read only
12/6/2018

28. Thank you
12/6/2018