Epithelia vary in permeability and this is down to whether the junction between them is tight or leaky. In leaky epithelia there is no transepithelial gradient maintained, or there is a low transepithelial electrical resistance so most solutes and water are transported in an isosmotic fashion. Examples of where leaky epithelia are found include the proximal tubule of the kidney and the small intestine. In general, leaky epithelia have few tight junction strand numbers and this means they have a low resistance.
- ↑ Boron W, Boulpaep E. 2009, Medical Physiology, 2nd edition, Philadelphia, Saunders Elsevier, Section II Chapter 5 page 142