Frequently Asked Questions: Excretory System

Q. How much blood does the kidney filter every day?
A. About 2000 litres

Q. Why do people urinate more in winter than summer, though they drink the same amounts of fluid?
A. Through sweat, our skin helps to regulate our bodies' water levels. The kidneys which make urine also help. In summer, we lose a lot of water through sweating and therefore do not urinate as much as we do in winter when we don't sweat as much.

Q. Indy and Formula One racing car drivers seem to drip with perspiration after a race. Why?
A. They do a lot of hard work driving at speeds up to 400 kilometres per hour. For example, Indy car drivers lose 3 litres of sweat during the race.

Q. Urine is sterile. Does this mean you can drink it without ill effects?
A. No. Sterile means that urine inside the body contains no bacteria. However as it passes out of the body, it will pick up bacteria on our skin. Also urine contains excess water, excess salt, and two nitrogenous wastes called urea and uric acid. If you drank urine, you would be drinking the wastes that your body had eliminated, and your body would then have to expend effort to eliminate them again.

Q. Why does skin wrinkle in water?
A. Water soaks into the callus of the skin in areas such as hands and feet where it is particularly thick, and causes distortion.

Q. How do deodorants work?
A. Deodorants work in either of two ways. Firstly, they may reduce your perspiration. Secondly, they may kill bacteria. It is the bacteria who make most of the body odour by breaking down fats on the skin into smelly fatty acids.