ABSTRACT
With respect to osmoregulation, birds differ in a number of aspects from the other group of warmblooded vertebrates—mammals. These differences are highlighted along with the organs and organ systems that function in osmoregulation in birds. These systems are the kidneys, lower gastrointestinal tract, and the nasal salt glands, and each is discussed in turn. As a class of vertebrates, birds have evolved successfully to inhabit almost all environments or biomes that occur on Earth. The gross morphology of the avian kidney differs markedly from the typical bean shape of the unipapillate kidney of small mammals. The paired avian kidneys fit tightly into the fused lumber and sacral vertebrae, and the tissue of each kidney is divided into three divisions: anterior, middle, and posterior, with the posterior divisions being the largest. The kidney is supplied with two afferent blood supplies: the typical high-pressure arterial supply and an afferent venous supply by way of a functional renal portal system.
