A tight junction is a specialized connection between adjacent cells that forms a barrier to regulate the passage of substances. These junctions are crucial in maintaining the integrity of tissues, particularly in epithelial cells, which line surfaces and cavities in the body. By preventing the leakage of materials between cells, tight junctions help control what enters and exits the bloodstream and other compartments. Tight junctions are composed of proteins, such as claudins and occludins, that interact to create a seal. They play a vital role in various organs, including the intestines, where they help absorb nutrients while blocking harmful substances. Dysfunction in tight junctions can lead to conditions like inflammatory bowel disease and other health issues.