The gastrointestinal tract, a specialized organ, maintains a dynamic balance between host cells and the external environment, including food digestion. The intestinal epithelial layer, along with the mucosal layer and the cellular immune system, forms the primary physical barrier against external factors and maintains a symbiotic relationship with commensal bacteria. Tight junction proteins, such as occludin, claudins, and zonula occludens, are crucial for maintaining epithelial barrier integrity. Intracellular signaling transduction systems and extracellular stimuli like cytokines, small GTPases, and post-translational modifications dynamically modulate tight junction protein complexes to allow essential molecule transport and restrict harmful substances. Imbalances in these regulations lead to compromised barrier integrity, contributing to inflammatory bowel disease, obesity, and metabolic disorders. Understanding the role of diseases in barrier integrity and the underlying regulatory mechanisms has improved our understanding of the intestinal barrier, paving the way for novel therapeutic approaches.The gastrointestinal tract, a specialized organ, maintains a dynamic balance between host cells and the external environment, including food digestion. The intestinal epithelial layer, along with the mucosal layer and the cellular immune system, forms the primary physical barrier against external factors and maintains a symbiotic relationship with commensal bacteria. Tight junction proteins, such as occludin, claudins, and zonula occludens, are crucial for maintaining epithelial barrier integrity. Intracellular signaling transduction systems and extracellular stimuli like cytokines, small GTPases, and post-translational modifications dynamically modulate tight junction protein complexes to allow essential molecule transport and restrict harmful substances. Imbalances in these regulations lead to compromised barrier integrity, contributing to inflammatory bowel disease, obesity, and metabolic disorders. Understanding the role of diseases in barrier integrity and the underlying regulatory mechanisms has improved our understanding of the intestinal barrier, paving the way for novel therapeutic approaches.