Paracellular transport refers to the transfer of substances between cells of an epithelium.
It is in contrast to "transcellular transport", where the substancees travel through the cell, passing through both the apical membrane and basolateral membrane.
The distinction is in particular significance in renal physiology. Transcellular transport is more likely to involve energy expenditure than paracellular transport.
Capillaries of Blood Brain Barrier have transcellular transport only in contrast with normal capillaries which have both - transcellular and paracellular transport. This is due to the presence of tight junctions in Blood Brain Barrier and Astrocytes that surround the capillaries.
- Essentials of Human Physiology by Thomas M. Nosek. Section 7/7ch05/7ch05p05.