Avian salt glands
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The processes involved at the apical and basal cell membranes in the formation of the hypertonic sodium chloride secretion in marine birds are discussed. Recent work indicates that the concentration gradient is established across the apical, i.e. luminal membrane probably by a sodium pump. There is also some evidence to suggest that during secretion, the uptake of sodium and chloride by the cell across the basal membrane may not be passive but may involve the exchange of sodium for hydrogen ions and chloride for bicarbonate. There is also the possibility that potassium secretion at high concentrations in some marine and desert species may involve an active extrusion across the apical membrane. Stimulation of secretion by acetylcholine and the possible effects of hormones on the secretory mechanism are considered.