Tight junctions are specialized connections between adjacent cells that create a barrier to prevent the passage of substances between them. They are primarily found in epithelial tissues, which line surfaces and cavities in the body. By sealing the space between cells, tight junctions help maintain the distinct environments on either side of the tissue, such as in the intestines and blood-brain barrier. These junctions are formed by proteins called claudins and occludins, which interact to create a tight seal. This structure is crucial for regulating the movement of ions and molecules, ensuring that essential nutrients are absorbed while harmful substances are kept out.