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, such as those lining the intestines and blood vessels, where they help maintain the integrity of the tissue and regulate what enters or leaves the body. These junctions are formed by proteins that interlock, sealing the space between cells. This allows tight junctions to control the movement of ions and molecules, ensuring that essential nutrients are absorbed while harmful substances are kept out. They play a crucial role in maintaining homeostasis within the body.