Excretion as an example of homeostatic Control: (Liver) Flashcards
Nitrogenous waste in Reptiles and Birds:
Eliminate their nitrogenous waste as uric acid, requiring more energy to synthesise but is less toxic and requires less water to flush.
Nitrogenous waste in aquatic animals:
Excrete their nitrogenous waste as ammonia which will passively diffuse into the surrounding environment (due to its high water solubility)
Nitrogenous waste in mammals:
Mammal convert their nitrogenous waste into urea via the ornithine cycle, which is less toxic than ammonia and less soluble.
Why is defecation not considered excretion:
Faeces is undigested food remnants, not metabolic waste products.
What are the two functions of the excretory system?
- Removal of nitrogenous waste
- Removes water to maintain suitable osmolarity
what are the key metabolic waste products:
CO2, Bile pigments (from old red blood cells), Nitrogenous waste products (urea), Excess water
Carbohydrate Metabolism:
Excess glucose is taken up by the liver and stored as glycogen. When blood levels drop the liver breaks down glycogen into glucose and exports it to body tissues. When hepatic glycogen reserves run out, the liver synthesises glucose from other sources. These processes are controlled by insulin and glucagon.
Deamination:
amino acids are broken down when in excess + can’t be stored.
Amine + hydrogen -> ammonia -> reacts with CO2 to form urea.
Transamination:
Conversion of one amino acid into another
Detoxification:
The breakdown of not needed or toxic substances by the liver.
What substances in animals must undergo detoxification:
Urea, lactate, alcohol, hormones, medicinal drugs, hydrogen peroxide.
Metabolism of hydrogen peroxide:
Hepatocytes contain catalase to convert hydrogen peroxide into water and oxygen.
Hormone metabolism:
Protein hormones and peptide hormones are hydrolysed into amino acids which can then be converted to urea.
Lactate Metabolism:
Lactate can be used for anaerobic respiration. Lactate can also be absorbed by hepatocytes and converted into pyruvate (an intermediate molecule for aerobic respiration.)
Alcohol Metabolism:
Alcohol in the blood is taken by hepatocytes and is respired by hepatocytes. The alcohol is broken down by an enzyme called alcohol dehydrogenase to convert ethanol to ethanal and then ethanoate.