College Answer
This is a very straightforward question testing breadth of knowledge rather than depth. It was well answered by the majority of candidates.
Discussion
This is only a straightforward question if the savvy candidate had thought deliberately about it prior to the exam, as this whole vast massive range of functions does not spontaneously coalesce into a ten-minute answer in one's mind. It really needs a bit of preparation. Fortunately, it has come up many times, and we should all be warned that it will surely appear again.
- Storage functions of the liver:
- Metabolic fuel storage: glycogen (75g, 400kcal) and fat (75g, 600 kcal)
- Vitamin storage: fat soluble A, D, E and K, as well as B12
- Trace element storage: iron (as ferritin), copper, sink, selenium
- Blood reservoir function: contains up to 27% of total blood volume
- Synthetic functions of the liver:
- Synthesis of 90% of blood proteins (albumin, clotting factors, complement)
- Synthesis of regulatory molecules (thrombopoietin, angiotensinogen)
- Synthesis of nutrients: glucose (gluconeogenesis), ketones, lipids (VLDL), cholesterol, non-essential amino acids
- Synthesis of bile acids from cholesterol and urea from ammonia
- Synthesis of bilirubin (by Kupffer cells)
- Metabolic functions of the liver:
- Carbohydrate metabolism: conversion to and from glycogen
- Lipid metabolism: transformation into ketones or triglycerides
- Protein metabolism: deamination or transamination of amino acids
- Ammonia metabolism (into urea) and lactate metabolism (into glucose)
- Immunological functions of the liver:
- Synthesis of complement proteins (innate immunity)
- Regulation of protein synthesis to hinder infection (eg. restriction of systemic iron carriage and reduced production of negative acute phase reactants)
- Filtration of antigens from the blood by Kupffer cells and sinusoidal endothelial cells
- Excretory functions of the liver:
- Excrretion of bile acids (though 95% undergo reabsorption)
- Excretion of cholesterol in the bile (800-1200mg/day)
- Excretion of conjugated bilirubin in the bile
- Excretion of some ions (mainly sodium)
- Biliary excretion of drugs (ceftriaxone, apixaban, digoxin)
- Biliary excretion of heavy metals (lead, arsenic, mercury, cadmium)