5-2-1-the-importance-of-excretion

The Importance of Excretion

• Excretion is the process by which toxic waste products of metabolism and substances in excess of requirement are removed from the body

• For example:

  • The lungs excrete the waste product carbon dioxide by gas exchange and the act of breathing out (exhalation)

  • The kidneys produce urine that contains the waste product urea in solution

• Excretion is a key process in homeostasis and is important in maintaining metabolism, as metabolic waste can have serious negative consequences on the body if allowed to accumulate

Metabolic waste

• As mammals are active, warm-blooded animals, they have high metabolic rates, which means they also produce relatively large amounts of metabolic waste

• This metabolic waste includes:

  • Carbon dioxide

  • Nitrogenous waste (ammonia, urea and uric acid)

  • Bile pigments (produced during the breakdown of haemoglobin)

• Carbon dioxide is produced from the decarboxylation of respiratory substrates

• Ammonia is produced from the deamination of excess amino acids

• If these two waste products are not excreted properly, they can accumulate and change the cytoplasm and body fluid pH, which can cause enzymes to work less efficiently

• The effects that different metabolic wastes can have on the body if allowed to accumulate are summarised in the table below

  • Note that the liver is a key organ in producing all of these excretory substances (except for carbon dioxide)

Metabolic Wastes Table