Tight Junctions
Plain-English definitions of microbiome research vocabulary — the terms you'll see across articles, testing services, and probiotic claims.
Protein structures that seal the gaps between intestinal epithelial cells, controlling what passes from the gut lumen into the bloodstream. Disruption of tight junctions — by stress, certain bacteria, or dietary factors — increases intestinal permeability and is a key mechanism in gut barrier dysfunction.
Related terms
Intestinal Permeability
The property of the intestinal lining that controls what passes from the gut into the bloodstream. Increased permeability (sometimes called "leaky gut") allows harmful substances to enter circulation, triggering immune responses.
Zonulin
A protein that regulates the tight junctions between intestinal cells. Elevated zonulin levels increase intestinal permeability. Discovered by Alessio Fasano, zonulin is triggered by gluten exposure and certain bacteria, and is studied as a biomarker for gut barrier function.