Chapter 6 - Water Balance and Gas Exchange

Abstract

Because amphibians and reptiles live on land, in fresh water, and in salt or brackish water, a wide range of physiological mechanisms helps to maintain ionic homeostasis in body fluids. Homeostasis is generally maintained by movement of water and/or ions into and out of the body, involving kidneys, specialized salt glands, and respiratory surfaces. Water loss is a major challenge for amphibians because water easily is lost through their skin. Many examples reveal the diversity of mechanisms used by these animals to maintain homeostasis, including a particularly interesting mechanism in the desert tortoise. Water loss and gas exchange are tied together because significant water loss occurs across respiratory surfaces and gas exchange cannot occur without a wet surface across which oxygen and carbon dioxide can move.