liver

• what is excretion?


  removal of toxic or excess waste products of metabolism produced by cells from the body
• what is egestion?


  removal of unwanted material from the body e.g. undigested food, only faeces
• what are the main excretory products?

  carbon dioxide, Urea, Bile pigments
• why must excess carbon dioxide be removed?

  Low blood PH- reacts with water to form carbonic acid which lowers blood PH and affects enzyme activity

  Reduced capacity to carry oxygen - carbon acid formed inside RBCs disassociates to produce H+ that causes oxygen to dissociate

  Reduced affinity of haemoglobin for oxygen- co2 combines with Hb to form carbominohaemoglobin
• what is the role of the liver in homeostasis?

  regulates concentration of substances e.g. glucose and amino acids in the blood

  removes toxic substances that would affect cell enzyme activity
• which blood vessels carry blood to the liver?

  hepatic portal vein

  hepatic artery
• why does the liver have 2 blood supplies?


  hepatic artery carries oxygenated blood for aerobic respiration for ATP for metabolic processes .

  Hepatic portal vein carries deoxygenated blood containing products from digestion. liver removes the excess glucose, amino acids and alcohol
• which blood vessel returns blood to the circulatory system?


  Hepatic Vein
• where is bile stored and produced?


  produced in the liver, stored in the gall bladder
• what are the main roles of Bile?


  contains bile pigments e.g. bilirubin from haemoglobin

  contains bile salts which emulsify fats to increase surface area for fats
• what is the role of kupffer cells?


  star shaped, engulf, breakdown and recycle old red blood cells
• describe how the structure of the liver ensures blood flows past as many hepatocytes as possible and relate this to liver function?


  divided into lobes which are then divided into lobules ... many sinusoids leasing to a central vein

  sinusoids lined with thin endothelic cells
• what is the difference between a sinusoid and a canaliculus?


  sinusoid carries blood toward the centre of the lobule and connect with the blood vessel. also lined with endothelial cells which give a short diffusion distance as fenestrations are large

  canaliculi- carry bile towards the outside of lobule, only have one exit... goes to the gall bladder
• name features of hepatocytes?

  many mitochondria- to produce ATP for metabolic processes

  RER- to allow protein synthesis to produce plasma proteins

  glycogen granules- break down into glucose to regulate blood glucose levels

  lipid droplets - used in aerobic respiration, hydrolysed for energy

  microvilli - large surface area for absorption
• how is glycogen adapted for storage of glucose?

  compact, highly branched, enzymes insoluble so water potential isn't affected
• describe the formation of urea?

  excess amino acids that can't be stored are deaminated by the removal of an amine group.

  The keto acid formed enters aerobic respiration to produce ATP or used in lipid storage

  The ammonia formed is very toxic and soluble, so is rapidly combined with carbon dioxide to form urea in the ornithine cycle
• what is the word equation to summarise deamination of an amino acid?

  amino acid+oxygen = Keto acid + ammonia
• what is the word equation for the formation of urea?

  ammonia +carbon dioxide = urea + water
• suggest why fish can excrete ammonia but the ammonia is converted into urea for excretion in mammals?

  ammonia is very soluble and more toxic than urea. Fish can rapidly dilute the ammonia in a large volume of water and immediately remove it from the body while mammals can't
• what are the advantages and disadvantages to mammals of excreting urea?

  mammals must conserve water and urea is less toxic so it can be safely transported in the blood plasma and be filtered out

  disadvantage is that it requires ATP so has an energy cost
• what is detoxification?

  conversion of toxic molecules to less toxic or non toxic molecules
• give 3 examples of substances that are detoxified by the liver?

  breakdown of hydrogen peroxide by enzyme catalase (inside peroxisomes)

  breakdown of drugs by cytochrome P450 (paracetamol)

  Ethanol
• why is ethonol broken down and products respired?

  toxic

  contains chemical potential energy that can be used to synthesis ATP in aerobic respiration
• describe the process of detoxification in Ethanol?

  Ethanol is oxidised to ethanal by the enzyme ethanol dehydrogenase and one NAD becomes reduced.

  Ethanal is then oxidised to produce Ethanoate by ethanal dehydrogenase and another NAD is reduced

  Ethanoate is then converted to acetyl coA
• what other processes apart from detoxification require lots of NAD?

  aerobic respiration - Krebs cycle, oxidative phosphorylation, link and glycolysis

  and beta oxidation of fatty acids
• describe the process of how excess alcohol can lead to the condition known as fatty liver?

  Ethanol diffuses directly through the plasma membrane of the hepocyte

  Ethanol is toxic to the cell contents so must be detoxified

  Ethanol is first oxidised to ethanal. catalysed by ethanal dehydrogenase.

  The enzyme ethanal dehydrogenase then used NAD to oxidise ethanol to ethanoate.

  stores of NAD are used up, so there is insufficient NAD remaining for the breakdown of fatty acids

  therefore, fatty acids are converted back into triglyceride and stored in hepocytes
• suggest why enzymes are concentrated in the endoplasmic reticulum in detoxification of drugs?

  enzymes are synthesised on ribosomes attached to RER and transported e.g. act in SER

  paracetamol inhibits the enzyme COX involved in prostoglandin synthesis occurs in SER

  cytochrome p450 and enzymes associated with paracetamol detoxify
• suggest why many drugs have different side effects?

  different alleles of P450 gene code for different versions of the enzyme. (different primary structure)

  enzyme altered tertiary structure different levels of activity of produce different products
• explain why bilirubin production and processing is an example of excretion?

  bilirubin is a metabolic waste product of the breakdown of harm from haemoglobin in worn out red blood cells and is removed from the body via faeces