The jejunum is the middle segment of the small intestine, located between the duodenum and ileum. Its epithelial lining is composed mainly of enterocytes sealed by tight junctions (claudins, occludin, ZO proteins), which regulate the paracellular pathway. The jejunal mucosa is highly permeable compared with more distal regions, facilitating rapid absorption of nutrients, electrolytes, and water. Proximal jejunum generally shows higher baseline permeability than the ileum.<\/p>
Transport across the jejunal barrier involves passive diffusion, carrier-mediated uptake, and regulated paracellular flux. Uptake transporters such as peptide transporter 1 (PEPT1), sodium-glucose cotransporter 1 (SGLT1), and LAT1 facilitate entry of dipeptides, sugars, and amino acids. Efflux proteins, most notably P-glycoprotein (ABCB1) and breast cancer resistance protein (BCRP\/ABCG2), actively expel xenobiotics and many drugs back into the lumen, reducing systemic exposure.<\/p>
This combination of absorptive and protective mechanisms ensures efficient nutrient uptake while restricting potentially harmful compounds. Disruption of tight junctions or dysregulation of transporters, as seen in inflammation or disease, increases barrier leakiness and alters bioavailability. Because of its high absorptive efficiency and dynamic transporter activity, the jejunum is central to drug absorption and permeability studies.<\/p>
Characteristics of the human jejunum (ref. 10.1016\/S1359-6446(04)03354-9)<\/a><\/p>
Surface area (m2<\/sup>)<\/p><\/th> Segment length (cm)<\/p><\/th> pH of segment<\/p><\/th><\/tr> 184.0<\/p><\/td> ~280<\/p><\/td> 5.5-7.0<\/p><\/td><\/tr><\/tbody><\/table> <\/p> <\/p> |
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