Intercellular Junctions Lecture Notes

Introduction

• Intercellular junctions are formed by proteins in the plasma membrane.
• They create connections between cells in tissues.
• Three main types of junctions: tight junctions, desmosomes, and gap junctions.

Tight Junctions

• Structure: Proteins from adjacent cells fuse together, forming an impermeable barrier.
  • Cells are so close that solutes cannot pass between them.
  • Analogy: "Zipper" - cells connected tightly like a zipper.
• Function: Provides a barrier and lining function.
  • Important for epithelial tissues.
  • Examples: Skin, digestive system (e.g., stomach).
  • Prevents substances like hydrochloric acid from seeping between cells and causing damage.

Desmosomes

• Structure: Fibrous proteins that resemble threads.
  • Proteins extend from one cell to another, anchoring cells together.
  • Allows resistance against mechanical forces.
• Function: Provides mechanical strength, keeping cells together.
  • Known as mechanical junctions.
• Examples: Skin and heart.
  • In the heart, they prevent cells from falling apart during contractions.

Gap Junctions

• Structure: Proteins in the plasma membrane form pores/openings.
  • These pores connect adjacent cells, allowing solutes to pass directly between them.
• Function: Facilitates communication between cells.
  • Known as communicating junctions.
  • Allows quick transmission of electrical signals.
• Examples: Particularly important in the heart.
  • Facilitates synchronized contraction of heart cells by allowing them to communicate effectively.

Conclusion

• Each type of junction has a specific role despite being collectively called junctions.
• Tight junctions, desmosomes, and gap junctions have distinct functions critical to tissue integrity and communication.