Paracellular and Transcellular Routes for Water and Solute Movements Across Insect Epithelia

Because the frontal area of the intercellular clefts in Malpighian tubules is small, and the osmotic permeability of the cell membranes is large, the route for transepithelial water movement during fluid secretion is transcellular. Water movements appear to be a passive response to osmotic gradients of a few mosmol 1(-1) produced in the cells and in he lumen by active ion transport. The excretory functions of Malpighian tubules are discussed in …