ABSTRACT
In animal cells, the cell volume must remain close to constant; thus, the osmolality of the cytosol must be kept almost equal to that of the cell-surrounding medium to prevent water exchanges. Since studies conducted during the first part of the 20th century, solutes of the crustacean hemolymph have been known to include organic and inorganic compounds. Given their relative concentrations, it clearly appears that ions are the main osmotic effectors, accounting for over 90% of the hemolymph osmolality. One first adaptation in osmoregulation is the limitation of water and ion fluxes through reduction in the integumental permeability. The complete impermeabilization of the integument is impossible because it would be incompatible with respiratory gas exchanges and excretion of waste products. Early experiments based on changes in weight after blockage of excretory pores showed that osmoregulators are less permeable to water than osmoconformers.
