Question 11(p.2)

Outline the principal functions of the Liver, and give examples.

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College Answer

For a good answer candidates were expected to at least mention the following --
Formation and secretion of bile
Carbohydrate metabolism (Glycogen synthesis and breakdown, Gluconeogensis)
Lipid metabolism (Fatty acid oxidation, Synthesis of cholesterol and phospholipids,
Production of ketoacids)
Protein metabolism Breakdown
Metabolism of toxins, drugs (Phase I reactions - oxidation, reduction, hydrolysis,
Phase II reactions- conjugation/glucuronidation)
Storage (Vitamins B12, A, D 2, Iron as ferritin, Glycogen)
Immunity
Endocrine (Synthesis of 25 OH cholecalciferol, Metabolism of steroid hormones, Synthesis
of somatomedins, Erythropoietin)
Miscellaneous (Acid base role – lactate metabolism, Blood store)
Syllabus – I2a
Reference: Gannong p485, Power and Kam p185

Discussion

  • 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)

References

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.