The body constantly exchanges water with the environment. In a steady state, the intake of water equals its loss. The main source of water intake is oral and the main source of loss is the urine. We also lose water through the lungs, sweat and feces: this is called the 'insensible' water loss and amounts to approximately 500 mL daily (Fig. 22.6). Importantly, the insensible loss can increase substantially with high temperatures, during intensive exercise, and also as a result of diarrhea or fever.
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