solve the CHAPTER MYSTERY

(NEAR) DEATH BY SALT WATER

Luckily, the pick-up the group arranged arrived earlier than planned. They rushed the sick man to a hospital, where he was diagnosed with severe dehydration and given water and intravenous fluids. If he had gone much longer without treatment, doctors told his friends, he would have died. What had happened? Why didn't his friends suffer the same problems?

As sailors have known for centuries, humans can't drink seawater for any length of time. But why can't we drink seawater?

Because seawater is saltier than human blood and body fluids, drinking it loads the body with excess salt. Human kidneys cannot produce urine with salt concentrations high enough to get rid of that salt efficiently. So the kidneys are forced to excrete more water in urine than the amount of salt water consumed. This lowers body water content to the point that blood literally becomes thicker and harder to push through fine capillary networks. Cells and tissues begin to dehydrate, and fatal kidney failure can result.

1. Compare and Contrast While the group member who drank seawater became seriously ill, the other group members experienced some water stress as well. What was going on in their circulatory and excretory systems, and why was it not as serious?

2. Propose a Solution If you were marooned on an island that had no fresh water, what would be your plan for getting some?

3. Connect to the Although humans can't drink salt water, and can't exist without fresh water, many marine birds and reptiles can do either or both. Using the Web, research the different strategies other animals use to regulate salt content and water balance.