Excretion is the elimination of waste products from the body. The breakdown of different chemical substances in the body to release energy produces many waste products. As a result of digestion and other chemical processes taking place in the body, a large amount of carbon dioxide, water and nitrogen containing substances such as ammonia, urea and uric acid are produced. These wastes must be thrown out of the body from time to time.
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All the organs associated with the process of excretion make up the excretory system. Carbon dioxide and some amount of water vapor are easily got rid off as gases by exhalation. The skin eliminates water and some salts as sweat. Kidneys excrete nitrogenous (nitrogen containing) waste products and water as urine. The organs which form, store and get rid of urine make up the urinary system. In human beings the urinary system consists of the following organs:
- Kidney
- Ureters
- Urinary bladder and urethra.
1. Kidney:
Our body contains a pair of reddish brown, bean-shaped kidneys. The kidneys are located just below the diaphragm on either side of the backbone. Each kidney has numerous tiny filters that filer out the waste from blood and form urine. The urine thus formed is poured into two tubes called ureters which come out from the concave face of the kidney. An adult human being normally produces about 1-1.8 liters of urine in 24 hours. The volume of urine produced depends upon fluid intake, level of physical activity and temperature.
2. Ureters:
Ureters are a pair of thin muscular tubes arising from openings on the concave side of the kidney. They carry urine from kidneys to a bag-like urinary bladder.
3. Urinary Bladder and Urethra:
Urinary bladder is a hollow muscular sac. Urine from the two kidneys is drained into the bladder where it is stored temporarily. The wall of the bladder can be stretched considerably and its size depends on the amount of urine it contains. Urethra is the thin tube that arises from the neck of the bladder and carries urine outside the body.