The Salt-Secreting Gland of Marine Birds

Marine birds possess salt-secreting nasal glands which produce hypertonic solutions of sodium chloride in response to osmotic loads such as ingestion of sea water. The concentration of the secreted fluid is always high, several times as high as the maximum urine concentration in birds. The presence of this gland must be considered a necessary adaptation to marine life in animals whose kidney cannot excrete high salt concentrations. The structure and blood supply to the gland indicate a countercurrent flow, but at the moment it is not possible to explain the high concentrations of the secreted fluid as the result of a countercurrent multiplier system. The gland is under parasympathetic nerve control; its secretory function is blocked by anesthesia and certain drugs, including carbonic anhydrase inhibitors.