Biochemistry of the liver Flashcards
What are the functions of the liver?
Bile production
Elimination of unwanted molecules
Secretion of plasma proteins
Storage of important molecules
Which molecules, of endogenous origin, are excreted in the bile?
Steroid hormones
Bilirubin
Which molecules, of exogenous origin, are excreted in the bile?
Lipid soluble substances ingested as drugs
What happens to drugs that are metabolised in the liver?
Made more polar to make excretion easier
What is the function of cytochrome P-450 enzymes?
They catalyse the phase 1 reaction of metabolism in the liver - changing an unwanted molecule to a derivative e.g. by oxidation or hydroxylation
What is phase 2 of liver metabolism?
Conjugation of new OH group on derivative
Give an example of a drug which can cause hepatotoxicity through production of a toxic metabolite.
Paracetamol
In paracetamol overdose, what pathway is overwhelmed and what does this result in?
Conjugation pathway is overwhelmed, so toxic metabolite builds up in liver causing hepatocellular damage
What causes prehepatic jaundice?
Excess production of bilirubin due to haemolysis
What might cause posthepatic jauncide?
Bile duct obstruction e.g. gallstone
Why might you get pale stools and dark urine in post hepatic jaundice?
Pale stools due to reduction of faecal bile pigment
Dark urine due to excretion of water soluble bilirubin conjugates
What causes intrahepatic jaundice?
Generalised hepatocyte dysfunction
What is the treatment for intrahepatic jaundice in neonates?
Phototherapy with blue-white light
Isomerises bilirubin to more soluble form which can be excreted in bile
After a meal, which pathway is excess glucose diverted towards?
Pentose phosphate pathway to make NADPH for biosynthetic processes
Where are amino acids for gluconeogenesis taken from in the postabsorptive state?
Muscle protein is degraded to provide amino acids
Where does glycerol used in gluconeogenesis come from?
Glucagon stimulates lipolysis by hormone-sensitive lipase
What happens to the fatty acids after lipolysis in the postabsorptive state?
Fatty acids metabolised, ketone body formation increases
What are ketone bodies used for?
Used as a source of energy by heart and skeletal muscle
What is the main energy substrate in the starving state?
Fatty acids
What can the brain adapt to use as fuel instead of glucose in the starving state?
Ketone bodies
What are the functions of plasma proteins?
Maintenance of oncotic or colloid osmotic pressure
Transport of hydrophobic substances e.g. sterioid hormones, free fatty acids, bilirubin and cholesterol
pH buffering
Enzymatic e.g. blood clotting
What are the functions of alpha globulins?
Transport lipoproteins, lipids, hormones and bilirubin
e.g. ceruloplasmin or retinol binding protein
What are two examples of beta globulins and what do they do?
Transferrin - transports Fe3+ and is an indicator of iron deficiency
Fibrinogen - inactive form of fibrin, causes clotting of blood when activated
What is the most abundant plasma protein?
Albumin
