Understanding Cell Junctions and Their Functions

Aug 9, 2024

Cell Junctions Lecture Notes

Introduction

  • Overview of cell junctions.
  • Encouragement to like, comment, subscribe, and check website for additional resources.

Chegg Study Tools

  • Mention of Chegg resources for studying.
  • Example of how to utilize Chegg for exam preparation (Organic Chemistry).
  • Importance of understanding concepts through provided materials.

Cell Junctions Overview

  • Definition: Adhesions that form between cells.
  • Functions:
    • Resist separation due to shearing forces (e.g., stretching, abrasiveness).
    • Block ions from moving between cells (diffusion barrier).
    • Facilitate communication through channels.
    • Connect cells to extracellular matrix (basal lamina).

Types of Cell Junctions

  1. Tight Junctions

    • Proteins involved: Occludins, Claudins, Zona Occludens.
    • Main function: Act as a diffusion barrier.
    • Location: Primarily at the apical surface of cells.
    • Clinical relevance:
      • Blood-brain barrier: Prevents harmful substances from entering neural tissue.
      • GI tract: Prevents pathogens and large molecules from absorbing into the bloodstream.
      • Stomach: Protects against hydrochloric acid damage.
      • Leaky junctions in the kidneys allow selective ion passage.
      • Pathogens like Helicobacter pylori and Clostridium difficile can disrupt tight junctions leading to diseases like peptic ulcer disease and C. diff associated diarrhea.

  2. Adherence Junctions

    • Components: E-cadherins, Calcium ions, Vinculin, Catenin, Actin filaments.
    • Function: Provide resistance to shearing forces and stretching.
    • Location: More basal than tight junctions.
    • Clinical relevance:
      • Found in GI tract, respiratory tract, urinary system, blood vessels, skin.
      • Mutations in cadherin proteins can lead to metastasis in cancer.

  3. Desmosomes

    • Components: Desmoglein, Desmocollin (cadherins), Desmoplakin, Intermediate filaments (Keratin).
    • Function: Provide strong adhesion and resistance to shear forces.
    • Location: Common in cardiac tissue (intercalated disks) and skin.
    • Clinical relevance:
      • Pemphigus vulgaris: An autoimmune disease resulting in blistering due to destruction of desmosomes.

  4. Hemidesmosomes

    • Not a true cell-to-cell junction; connects cells to the extracellular matrix (basal lamina).
    • Components: Integrins, Intermediate filaments (Keratin).
    • Function: Anchor epithelial cells to basal lamina.
    • Clinical relevance:
      • Bullous pemphigoid: An autoimmune disorder causing blistering due to destruction of hemidesmosomes.

  5. Gap Junctions

    • Structure: Composed of connexons (made of connexins).
    • Function: Allow for cell-to-cell communication (ion and small molecule transfer).
    • Important in tissues that require coordinated activity:
      • Cardiac tissue (propagation of electrical signals).
      • Smooth muscle tissue (coordinated contraction).
      • Certain neurons (electrical signaling).
    • Role in signaling for cellular responses (e.g., apoptosis, hypertrophy).

Conclusion

  • Summary of importance and functions of different cell junctions.
  • Emphasis on clinical relevance of understanding cell junctions.