What is the primary role of tight junctions in endothelial cells?

Tight junctions play a crucial role in regulating paracellular transport, which refers to the movement of substances between cells rather than through them. These specialized structures are composed of proteins that seal adjacent endothelial cells together, creating a barrier that limits the passage of ions and molecules. This is particularly important in maintaining the selective permeability of blood vessels, such as those in the brain, where the integrity of the blood-brain barrier is critical for protecting the central nervous system.

By controlling paracellular transport, tight junctions ensure that only certain substances can pass through the spaces between cells, thereby contributing to homeostasis and regulating the internal environment of tissues. This function is vital for processes such as nutrient absorption, immune responses, and preventing the entry of potentially harmful substances into the tissue spaces.

In this context, while structural support, communication between cells, and anchoring to the extracellular matrix are important cellular functions, they do not define the primary role of tight junctions in endothelial cells as effectively as the regulation of paracellular transport does.