Paracellular transport occurs through tight junctions and tends to involve which molecular size?

Paracellular transport occurs through tight junctions and tends to involve which molecular size?

• A. High molecular weight molecules
• B. Low molecular weight molecules
• C. Lipophilic molecules crossing membranes
• D. Proteins crossing via channels

Answer: (C)

Paracellular transport uses the spaces between epithelial cells, guarded by tight junctions. These junctions form pores that act as a size- and charge-selective barrier, so only small, water-soluble solutes and ions can pass through. Large molecules don’t fit these pores, and lipophilic molecules typically cross membranes by the transcellular route (through the cell) rather than between cells. So paracellular passage is characteristic of low molecular weight, hydrophilic solutes rather than high molecular weight compounds or lipid-soluble substances.

Paracellular transport uses the spaces between epithelial cells, guarded by tight junctions. These junctions form pores that act as a size- and charge-selective barrier, so only small, water-soluble solutes and ions can pass through. Large molecules don’t fit these pores, and lipophilic molecules typically cross membranes by the transcellular route (through the cell) rather than between cells. So paracellular passage is characteristic of low molecular weight, hydrophilic solutes rather than high molecular weight compounds or lipid-soluble substances.