Elimination of Wastes

The process of eliminating wastes from the body is called excretion. Waste materials are produced in the body due to metabolic activities. Some waste materials are also taken in from the environment. Elimination of waste materials is essential for maintaining homeostasis in the body.

Wastes include:

  • Heat
  • Metabolic waste products such as CO2, H2O, ammonia, urea, uric acid
  • Ions (Na+, Cl, HCO3)
  • Excess water
Organ/Systems Wastes Removed
Lungs CO2, Water, Heat
Skin Heat, Water, Salts, Urea
GI tract Solid wastes, CO2, Water, Salts, Heat
Lymph nodes & Spleen Bacteria, Dead RBCs
Kidneys Wastes containing nitrogen, Water, CO2, Salts, Ions

Carbon dioxide

Carbon dioxide is produced as a waste product from cellular metabolic activities. Carbon dioxide dissolves in body fluids and increases acidity. Thus, the body has to excrete it in appropriate quantities to maintain pH within the normal range. Carbon dioxide is excreted by the lungs during expiration.


Urine is formed by the kidneys. The urinary system consists of 2 kidneys, 2 ureters, 1 urinary bladder and 1 urethra. Urine consists of water and urea and other waste products which are produced from breakdown of proteins.

The kidneys regulate water balance in the body. They are play an important role in the regulation of the pH of the blood.


Feces is the waste from digestion of food. It contains:

  • Indigestible matter present in food
  • Bile produced by the liver
  • Microbes