Maintaining a stable internal environment, or homeostasis, is essential for the survival of complex animals. Living organisms must maintain a salt and water balance, and they must continually remove the toxic byproducts generated by metabolism.

Organisms have evolved a variety of strategies to maintain a more or less stable internal environment. In animals that have circulatory systems, the blood typically passes through excretory organs, commonly termed kidneys. In terrestrial animals, the kidneys not only play a major role in the removal of wastes but are also the primary organs of osmoregulation.

In this animation, we look at the function of the mammalian kidney.


The function of the mammalian kidney may be summarized as follows:

Mammals inhabit an enormous range of environments on Earth, including some of the most arid. The major adaptation that allows mammals to maintain homeostasis in the face of a wide range of osmotic stress is the variable ability of their kidneys to concentrate urine. Thus, when they take in lots of water in their food, they can excrete the excess water by producing dilute urine, and when they are exposed to very arid conditions, they can conserve water by producing a highly concentrated urine.

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Textbook Reference: Concept 36.5 Kidneys Adjust Water Excretion to Help Animals Maintain Homeostasis