Question 20

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)

Kuntz, Erwin, and Hans-Dieter Kuntz. "Biochemistry and functions of the liver." Hepatology Textbook and Atlas: History· Morphology Biochemistry· Diagnostics Clinic· Therapy (2008): 35-76.

Ozougwu, Jevas C. "Physiology of the liver." International Journal of Research in Pharmacy and Biosciences 4.8 (2017): 13-24.