🔬 Intestinal Tight Junction Permeability Simulator

Intact Tight Junctions Seal the Intestinal Epithelium

Claudins and occludin zip adjacent cells into a selective barrier.

• 100%: Junction Integrity (fully sealed apical complex)
• 4–8: Claudin Strands (parallel sealing strands per junction)
• <1 nm: Paracellular Gap (smaller than a water cluster)
• High: Barrier Resistance (transepithelial resistance at peak)

Claudin-occludin protein lattice

Claudins polymerize into strands that fuse neighboring membranes shut.

Over 20 claudin subtypes tune pore size per tissue.

Apical junctional complex

Tight junctions sit above adherens junctions near the cell apex.

ZO scaffold anchoring

Zonula occludens proteins tether junction strands to the actin cytoskeleton.

Selective Permeability Through Regulated Pores

Small ions slip through claudin pores while large molecules stay blocked.

• ~4 Å: Pore Diameter (sized for ions and water only)
• >180 Da: Molecules Blocked (sugars, peptides, toxins excluded)
• Charge-based: Ion Selectivity (claudin-2 pores favor cations)
• Pore + Leak: Flux Pathway (two distinct paracellular routes)

Pore pathway vs leak pathway

Charge-selective pores pass ions; a separate leak route restricts size.

Claudin-2 vs claudin-1 balance

Pore-forming claudins compete with sealing claudins for junction space.

Claudin-2 upregulation alone can double paracellular water flux.

Physiological regulation

Hormones and nutrients fine-tune pore claudin expression continuously.

Inflammation and Toxins Trigger Junction Loosening

Cytokines and bacterial toxins signal cells to unzip their tight junctions.

• TNF-α, IL-13: Key Cytokines (drive junction disassembly signaling)
• Elevated: Zonulin Release (endogenous modulator opens junctions)
• Increased: MLCK Activity (myosin contraction pulls junctions apart)
• Minutes–Hours: Onset Time (rapid signal-driven remodeling)

Cytokine signaling cascade

TNF-α activates MLCK, contracting the perijunctional actin ring.

Zonulin reversibly opens junctions within minutes of release.

Bacterial toxin exploitation

Pathogens hijack zonulin signaling to force their own entry.

Claudin redistribution

Sealing claudins internalize while pore-forming claudins stay put.

The Paracellular Space Widens Beyond Normal Limits

Actomyosin contraction physically pulls the intercellular gap wide open.

• 10–50 nm: Gap Width (up from under 1 nm sealed)
• >10,000 Da: Cutoff Raised (large proteins now fit through)
• Multiple: Strand Breaks (claudin strand network fragmenting)
• >70%: Resistance Drop (transepithelial resistance collapse)

Cytoskeletal ring contraction

Perijunctional actomyosin rings pull cell borders apart mechanically.

Strand fragmentation

Continuous claudin strands break into discontinuous, leaky segments.

A gap of just 10 nm already admits mid-sized proteins.

Loss of size selectivity

Pore and leak pathways merge into one open channel.

Barrier Dysfunction Lets Bacterial Fragments Leak Through

Undigested proteins and bacterial fragments cross freely into the bloodstream.

• Elevated: LPS Translocation (endotoxin enters systemic circulation)
• >100,000 Da: Size Blocked (almost nothing excluded now)
• Triggered: Systemic Inflammation (immune activation from leaked antigens)
• Leaky Gut: Clinical Link (associated with autoimmune conditions)

Bacterial fragment translocation

Lipopolysaccharide fragments cross the ruptured barrier into vessels.

Circulating LPS can trigger low-grade inflammation body-wide.

Immune activation cascade

Leaked antigens provoke innate immune responses far from the gut.

Chronic disease associations

Sustained barrier dysfunction is linked to IBD and metabolic disease.