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
