Medicine & USMLE

Tight Junctions

Cell Junctions
  1. Gap Junctions
  2. Tight Junctions
  3. Desmosomes


Tight Junctions, also called zonula occludens or occluding junctions, are cell junctions that function by knitting the membranes of two adjacent cells tightly together, forming a watertight barrier. These junctions are often found in locations exposed to fluids that they must contain - like the linings of the intestines, kidneys and the bladder. On the cellular level, tight junctions are created by coupling the actin Microfilaments of neighboring cells together.

Key Points

  • Tight Junctions
    • Also called zonula occludens or occluding junctions
    • Forms a watertight seal
      • Occludin proteins press plasma membranes of adjacent cells tightly against each other
      • Bound by cytoskeletal Microfilaments, made of actin
    • Found in the Intestines, Kidney/Bladder, and the blood brain barrier (BBB)
      • Impermeable barriers contain fluids, prevent leakage, and control absorption
      • Tight junctions fully encircle the apical area of every cell in the epithelial sheet to form a watertight layer