2.68a excretion

1. The kidneys excrete a molecule known as uria which contains nitrogen, which is toxic to the body and therefore cannot be stored. 
2. The original form of nitrogen circulating in our blood stream which is potentially toxic are the amino acids. 
3. Amino acids are used for growth, however, amino acids which are in excess must be removed because they're toxic. 
4. Blood circulates to the liver and the amino acids are broken down into the molecule called urea. 
5. The urea re enters the blood stream and to be removed by the body it circulates to the kidney. 
6. the kidneys filter the urea from the blood and the urea will be added to water to form urine. 
7. This urine drains down the uritus to collect in the bladder. 
8. The filtered blood, removed of the toxic amino acids, returns into the body through veins. 
9. This is called excretion