What is the function of tight junctions in animal cells?

Tight junctions play a crucial role in maintaining the integrity of tissue by preventing the leakage of extracellular fluid between cells. They form a selective barrier that controls the movement of substances across the epithelial layer, ensuring that materials must pass through the cells themselves rather than between them. This function is particularly important in tissues that line cavities and organs, such as the intestines and kidneys, where the regulation of substances is critical to maintaining homeostasis. Tight junctions effectively create a seal that helps in maintaining the distinct composition of the internal environment of the tissue compared to the external environment, making them essential for proper cellular function and organismal health.