1. In human beings during metabolic activities many waste products like water, nitrogenous compounds like ammonia, urea, uric acid, bile pigments, excess salts, etc. the toxic wastes are produced. 

2. To excrete all these waste materials in human beings there is an excretory system consisting of a pair of kidneys, a pair of ureters, urinary bladder and urethra. 

3. Each kidney is made up of more than one million nephron. These are the structural and functional units of excretory system. 

4. Per day 170 litres of water is filtered by kidneys. Out of this 168.2 litres is reabsorbed. This is a wonderful mechanism.

5. Total amount of urine excreted per day is about 1.6 to 1.8 litres. 

6. The kidneys have a great reserve power. If one kidney is removed due to disease or damage, the other kidney can take up the function of both the kidneys. 

7. It is so amazing that the 10 cm in length, 5-6 cm in breadth and 4 cm thickness size of the kidney can do filtration of blood and can remove all the poisonous substances from the human body and keeping the organism healthy. 

8. Skin is also an excretory organ responsible for elimination of wastes in the form of sweat along with various toxins.