excretion as an example of homeostatic control

• what is excretion?

  The removal of metabolic waste from the body. This means the removal of unwanted products of cell metabolism from the body.
• what are the main excretory products of the body?

  Carbon dioxide from respiration

  Nitrogen containing compounds like Urea

  Other compounds like bile pigments found in Faeces
• what are the main organs involved in excretion?

  The lungs

  The liver

  The kidney

  The ureter

  The bladder

  The urethra
• explain how the lungs are involved in excretion?

  Every living cell in the body produces carbon dioxide as a result of respiration. Carbon dioxide is passed from the cells of respiring cells into the blood stream, where as hydrogencarbonate ions it is transported to the lungs. In the lungs, the carbon dioxide diffuses into the alveoli to be excreted as the organism breathes out.
• explain how is the liver involved in excretion?

  The liver is directly involved in excretion. It has many metabolic roles and some of the substances produced will be passed into the bile for excretion with the faeces- like the pigment called Bilirubin. The liver is also involved in converting excess amino acids into urea. Amino acids are broken down by the process of deamination. The nitrogen containing part of the molecule is then combined with Carbon dioxide to make urea.
• explain how the kidneys are involved in excretion?

  the urea from the liver will be passed into the bloodstream to be transported to the kidneys. Urea is transported in solution, dissolved in the plasma of the blood; in the kidneys, the urea is removed from the blood to become a part of the urine. Urine is then stored in the bladder before being excreted from the body via the urethra.
• how is the skin involved in excretion?

  Excretion is not the primary function of the skin. Sweat contains a range of substances including, salt, urea, water, uric acid and ammonia. Urea, uric acid and ammonia are all excretory products. The loss of water and salts may be an important part of homeostasis- maintaining the body temperature and water potential of the blood.
• why is the process of excretion important?

  Allowing the products of metabolism to build up can be fatal. Some metabolic products such as carbon dioxide and ammonia are toxic. these products interfere with cellular processes by altering the pH, so that normal metabolism is prevented. Other metabolic products may act as inhibitors and reduce the activity of essential enzymes