1. Excretory System

2.  This system removes wastes from the body. Some animals remove excess water, salt, and other waste through their skin in the form of sweat.  Carbon dioxide is removed in some animals through the lungs as they breathe.  Nitrogen wastes are carried away from cells by the bloodstream. The liver filters these nitrogen wastes and converts them into urea. Urea is carried by the blood to the kidneys which filter it and other wastes from the blood.

3. Excretory System  Kidneys remove waste from the blood using millions of tiny filters called nephrons. Nephrons have membranes that allow some substances to pass through, but not others. They collect waste and send any useful substances back into the blood.  Kidneys produce urine from excess water and the collected wastes from the nephrons. Urine flows from the kidneys to the bladder. Once the bladder is full, urine leaves the body through a tube called the urethra.

4. What are three ways humans remove wastes?  Humans remove excess water, salt, and other wastes by sweating, humans breathe out carbon dioxide, and remove excess water and collected wastes from the kidneys as urine.

5. What do the kidneys do?  They filter wastes from the blood to produce urine.

6. Why are nephrons surrounded by many tiny blood vessels?  Nephrons have a membrane that allows some substances to flow in and out. Waste products are collected by the nephrons, and useful substances such as nutrients are passed to the blood through blood vessels.