Cell Junctions

Cell junctions are structures that connect cells to other cells. They are prevalent in epithelial tissue. There are three major types of cell junctions:

1. Tight Junctions

• Function: Connect cells by forming a watertight seal.
• Structure: Acts like glue that tightly binds cells.
• Purpose: Prevents passage of water, ions, and molecules between cells.
• Locations:
  • Bladder
  • Intestines
  • Kidney
• Example: Ensures the bladder can hold urine without leakage.

2. Desmosomes

• Function: Connect cells, allowing some space for stress relief.
• Structure: Resemble spot welds that attach to the cytoskeleton.
• Purpose: Permits passage of water, ions (e.g., sodium, potassium), and other small molecules between cells.
• Locations:
  • Skin
  • Intestines
• Example: Provides durability and flexibility in tissues exposed to stress.

3. Gap Junctions

• Function: Connect cells with tunnel-like structures.
• Structure: Allow water and ions to flow between cells.
• Purpose: Facilitate the spread of action potentials and electrical coupling.
• Locations:
  • Cardiac muscle
  • Neurons
• Example: Enables the heart to beat by spreading action potentials.

Summary

• Tight Junctions: Watertight seals preventing intercellular passage of substances.
• Desmosomes: Spot welds that provide structural integrity under stress, allowing some permeability.
• Gap Junctions: Tunnels for direct cell-to-cell communication and electrical signal propagation.