N1i / 17B20 / 17A22 / 13B04: Function of the liver

17B20: Exam Report

Outline the functions of the liver.

86% of candidates passed this question.

This is a very straightforward question testing breadth of knowledge rather than depth. It was well answered by the majority of candidates.

17A22: Exam Report

Outline the functions of the liver.

56% of candidates passed this question.

Most candidates attempted a structure however did not expand the answers within the categories: e.g. a passing mention of glucose homeostasis is insufficient to score full marks for the carbohydrate metabolism category.

13B04: Exam Report

Briefly outline the functions of the liver.

88.9% of candidates passed this question.

This question was generally well   answered with a good response being in some structured format, e.g. a mention,  followed  by  a  description  for  each  function  of  the  liver.  For  questions  asking  to  outline  a particular  topic,  a  general  overview  of  the topic is  expected  and  not  merely  a “dot-point” list of  the functions  of  the  liver  without  actually  delving  into  the  way  the  liver  does  those  functions.  In  general  candidates  should  avoid making  broad-brush  statements, which  do not get them any marks like “the Liver  is  the major organ in the body”. Candidates  were expected  to  list,  and provide  an  overview  for each, function of the liver.

N1i /17B20 / 17A22 / 13B04: Outline the functions of the liver

Carb Metabolism

  • Glucose taken up by portal system to transport to hepatocytes
  • Glucokinase of hepatocytes converts glucose →G6P so that diffusion gradient maintained
  • Glycogen formed from G6P
  • Glycogen formation & breakdown controlled by Glycogen Synthetase & Glycogen Phosphorylase
  • ↑[portal blood sugar] = ↑[insulin] = glycolysis, ↑pyruvate dehydrogenase, ↑Acetyl CoA, ↑glycogen synthetase, inhibits gluconeogenesis & glycogenolysis
  • Gluconeogenesis allows maintenance of constant BGL, 1° for brain requirement

Lipid Metabolism

  • β-oxidation: FAs →Acetyl CoA which occurs in cytoplasm of all cells
  • Acetyl CoA →used as E, fat storage, ketone synthesis
  • FA synthesis (from Acetyl CoA)
  • Ketogenesis (from Acetyl CoA)
  • Cholesterol metabolism
    • Controlled by HMG-CoA
    • 80% of synthesised cholesterol is converted into bile
  • Bile production
    • 1L/day
    • Emulsifies dietary fats & vits ADEK for absorption

Protein Metabolism

Anabolic

  • Synthesises plasma proteins inc Albumin & clotting factors
  • Oxidative deamination of amino-acids

Catabolic

  • Amino acid degradation:
    • Transamination
    • Deamination
    • Decarboxylation
  • Breakdown of amino acids produces NH3 →liver converts this to Urea in Ornithine cycle
  • Creatinine synthesised by liver →used by skeletal m. for E

Metabolism Toxins/Drugs

  • Biotransformation of endogenous & exogenous compounds
Metabolism
  • Inactivation of hormones →steroid hormones (oestrogen, cortisol, aldosterone), thyroxine

Endocrine

  • Synthesis of 25 hydroxycholecalciferol from cholecalciferol in starvation, to be converted to calcitriol in kidney
  • Secretes angiotensinogen
  • Synthesises EPO in foetus
  • Metabolises steroid hormones & thyroxine

Storage

  • Vits ADEK, riboflavin, folic acid, B12
    • Vit A →10 month
    • Vit D →3 month
    • Vit B12 →12 month
  • Glycogen →400g
  • Blood 500mL
  • Iron storage →as ferritin
    • Hepatocytes have large amounts of Apoferritin (protein)
    • Apoferritin reversibly combines with iron
    • ∴acts as blood iron buffer

Immunological

  • RES – tissue macrophages & monocytes distributed throughout body
  • Kupffer cells of liver line sinusoids →remove bacteria, endotoxins, denature proteins

Acid-Base

  • Metabolism of lactate, ketones, NH3
  • Synthesis of Albumin (weak acid)