The importance of excretion

• What is excretion?


  Excretion is the process by which toxic waste products of metabolism and substances in excess of requirement are removed from the body.
• How do the lungs contribute to excretion?

  The lungs excrete the waste product carbon dioxide by gas exchange and exhalation.
• What waste product do the kidneys produce?

  The kidneys produce urine that contains the waste product urea in solution.
• Why is excretion important for homeostasis?

  Excretion is important in maintaining metabolism and preventing the accumulation of metabolic waste, which can have serious negative consequences on the body.
• What type of animals produce relatively large amounts of metabolic waste?

  Mammals, as they are active, warm-blooded animals with high metabolic rates.
• What are the main types of metabolic waste produced by mammals?

  The main types of metabolic waste include carbon dioxide, nitrogenous waste (ammonia, urea, and uric acid), and bile pigments.
• How is carbon dioxide produced in the body?

  Carbon dioxide is produced from the decarboxylation of respiratory substrates during aerobic respiration in mitochondria.
• How is ammonia produced in the body?

  Ammonia is produced from the deamination of excess amino acids in liver cells.
• What can happen if metabolic waste products are not excreted properly?

  If metabolic waste products are not excreted properly, they can accumulate and change the cytoplasm and body fluid pH, causing enzymes to work less efficiently.
• What are the effects of different metabolic wastes if allowed to accumulate in the body?

  • Carbon dioxide: Cells damaged if blood pH falls below normal range (acidosis).
  • Ammonia: Increases cytoplasm pH and interferes with metabolic processes.
  • Urea: Readily diffuses into cells, decreasing their water potential, causing them to absorb water by osmosis and expand until they burst.
  • Uric acid: May form crystals in joints, causing gout.
  • Bile pigments: Accumulate in the skin, turning it yellow (jaundice).
• What is the source of carbon dioxide as a metabolic waste product?

  The source of carbon dioxide is the decarboxylation of respiratory substrates during aerobic respiration in mitochondria.
• What is the source of ammonia as a metabolic waste product?

  The source of ammonia is the deamination of excess amino acids in liver cells.
• What is the source of urea as a metabolic waste product?

  The source of urea is the ornithine cycle in liver cells.
• What is the source of uric acid as a metabolic waste product?

  The source of uric acid is the breaking down of adenine and guanine (purines) in the liver.
• What is the source of bile pigments as a metabolic waste product?

  The source of bile pigments is the breaking down of the haem groups of haemoglobin in liver cells.
• How does the accumulation of ammonia affect the body?

  Ammonia increases cytoplasm pH and interferes with metabolic processes, such as respiration and neurotransmitter receptor function in the brain.
• What are the consequences of urea accumulation in cells?

  Urea readily diffuses into cells, decreasing their water potential, causing them to absorb water by osmosis and expand until they burst.
• What condition can result from the accumulation of uric acid in the body?

  Uric acid may form crystals in joints, causing gout, a very painful form of arthritis.
• What effect does the accumulation of bile pigments have on the skin?

  Bile pigments accumulate in the skin, turning it yellow, a condition known as jaundice.