cell junction ppt dr huma beenish (1).pptx

Medical

1. Cell junctions Dr Huma Beenish

2. Learning objectives  Define cell junctions.  Classify cell junctions .  Explain the structure of each type of cell junctions .  Discuss the importance of each type of junction in relation to its location

3. Cell junctions Local specializations/modifications of the cell membrane which contribute to cohesion and communication between adjacent cells.

4. TYPES Between cells. Tight junctions (Zonula occludens) Adherens junctions (Zonula adherens) Desmosomes. Between cells and matrix 4. Gap junction. Between cell and basal lamina Hemidesmosomes. Focal contact.

5. CLASSIFICATION OF CELL JUNCTIONS

6. ZONULA OCCLUDENS Location: Near the cell apex. Structure: Present in the form of a ring or circumferential band Seals off the outer leaflets of plasma membrane of adjacent cells.

7. Example: Tight junctions of intestinal epithelium OCCLUDING JUNCTIONS

8. ZONULA OCCLUDENS Not a continuous seal , but a series of focal fusions created by trans membrane protein Occludin Claudins Reinforced by Cytoplasmic zonula occludens proteins ZO1,2,3

9. TIGHT JUNCTION Each cell possesses integral membrane proteins that bind to similar proteins in the adjacent, forming a continuous “weld ” 05-05-2014 Dr Kaukab

10. ZONULA OCCLUDENS

11. Number of fusion sites determine the sealing capability of the Zonula occludens. Sparse, from 01 to few in epithelial cells of PCT of kidney. Partially permeable . Numerous in urinary bladder. Impermeable DISTRIBUTION

12. ADHESIVE OR ANCHORING JUNCTIONS Below the tight junctions Types Zonula adherens Fascia adherens. Macula adherens /Desmosomes Hemidesmosomes

13. ZONULA ADHERENS Structure Band or belt like junction encircling the entire cell no fusion of cell membrane. Gap between adhering membranes is 15 - 20nm, occupied by trans membrane adhesion molecule E-cadherin

14. ZONULA ADHERENS Extracellular portions of E-cadherin molecules bound to each other by Ca ions. Cytoplasmic side the tails of E-cadherin are linked to CATENIN and VINCULIN which in turn bind to actin filaments

15. Fascia adherens Fascia Adherens  are ribbon like structures that stabilizes non-epithelial tissue. They are similar in function to the Zonula Adherens  or  Adherens . The junction of epithelial cells. It's a broad intercellular junction in the transversal sections of an intercalated disc of cardiac muscle anchoring actin filaments.

16. DESMOSOMES / MACULA ADHERENS Spot Weld-like junctions help to resist shearing forces . Intercellular space is up to 30nm, occupied by Ca dependent trans membrane glycoproteins of Cadherin family Desmocollins Desmogleins

17. DESMOSOMES / MACULA ADHERENS Electron Dense disc shaped material attachment plaque having several anchoring proteins desmoplakins plakoglobins Intermediate filaments attached to attachment plaque Crucial to tissues that experience mechanical stress as in myocardium, bladder, GIT mucosa

18. DESMOSOMES / MACULA ADHERENS

19. HEMIDESMOSOMES Location: Provide increased adhesion to the basal lamina. Function: Present in epithelia which are subjected to abrasion & mechanical shearing forces Distribution: In the basal layers of stratified squamous epithelium.

20. HEMIDESMOSOME Structure: Trans membrane linker protein INTEGRINS Enter the basal lamina & interact with its proteins laminins & type IV collagen Intracellular portion of these integrins bind to DESMOPLAKINS & PECTINS

21. GAP / COMMUNICATING JUNCTION Protienaceous tubes that connect adjacent cells Function: Present in tissues where coordinated activity is required Allows diffusion of small molecules such as ions, amino acids and metabolites Distribution: Epithelia, nerves, smooth & cardiac muscle, astrocytes

22. GAP JUNCTION Structure: A disk- or patch-shaped structure (nexus) Individual unit – Connexons. The Connexons in one membrane link with those in the other to form continuous pores that bridge the intercellular gap Each Connexons formed by six gap junction proteins – Connexins Each gap junction is formed by tens/hundreds of Connexons

23. GAP JUNCTIONS: MODEL Increase in intacellular calcium or dec in pH leads to closing of connexons

24. FUNCTIONS Seal to prevent flow of materials Provide mechanical stability Guard against physical disruption Channels of communication

25. MEDICAL CORRELATION Connexin mutations in human disease. Several diseases occur when genes encoding connexins are mutated. Mutations in the  connexin 26  ( Cx26 ) gene , highly expressed in cells of the cochlea, are associated with  deafness .

26. SUMMARY

27. Lateral domain and its specializations

28. MEDICAL APPLICATION PEMPHIGUS VULGARIS various blistering diseases caused by abnormal desmosome function due to autoimmune reactions against specific desmogleins that reduce cell-to-cell adhesion

29. ZONULA OCCLUDENS PROTEINS target for certain common bacteria. The enterotoxin secreted by clostridium perfringens bind claudin molecules of intestinal cells,interfere with tight junctions and causes loss of tissue fluid in to lumen. Helicobacter pylori binds the extracellular domains of tight junction proteins in cells of stomach and disrupts signaling from the junction.

30. Thank you