Biochemistry · MU Pleven

67. Biochemistry of Liver. Metabolic processes. Metabolism of carbohydrates, pro- teins and lipids.

Covers the liver as the body's central metabolic hub, taking up nutrients from the portal vein and deciding whether to store, convert, synthesise or release them. It then works through carbohydrate handling (glycogen storage and breakdown, gluconeogenesis, the pentose phosphate pathway, galactose and fructose), protein turnover (transamination, the urea cycle, plasma protein synthesis) and lipid metabolism (lipogenesis, VLDL export, ketone bodies, bile acids). It closes with clinical consequences of liver damage and fatty liver.

Inside: 2 sections · 3 labelled pictures · 10 flashcards · 3 min

Topic 67 of 76 in the MU Pleven syllabus for Biochemistry (Medicine, Year 2). The free AceMed note covers it in 2 sections, about 386 words (3 min of reading), with 10 flashcards.

In this note

  1. Biochemistry of Liver. Metabolic processes. Metabolism of carbohydrates, proteins and lipids.
  2. Biochemistry of the Liver

Biochemistry of the Liver

The liver is the central metabolic hub of the body. It receives nutrients from the gut through the portal vein and decides whether to store, convert, synthesize, detoxify or release them into the blood. It maintains blood glucose, regulates protein and lipid metabolism, synthesizes plasma proteins, and performs detoxification.

Carbohydrate Metabolism in the Liver

  • The liver keeps blood glucose stable, especially between meals.
  • In the fed state: – Takes up glucose (via GLUT2, insulin independent). – Converts glucose to glycogen (glycogenesis). – Converts excess glucose to fatty acids and triglycerides (lipogenesis).
  • In fasting: – Breaks down glycogen (glycogenolysis). – Produces new glucose from lactate, amino acids, glycerol (gluconeogenesis).
  • The liver also runs the Pentose Phosphate Pathway: – Producing NADPH for fatty acid synthesis. – Producing Ribose-5-phosphate for nucleotide synthesis.
  • The liver handles galactose and fructose metabolism, converting them into intermediates of glycolysis.

So, the liver acts as the glucose buffer of the body.

Protein Metabolism in the Liver

  • The liver is the main site of amino acid turnover.
  • It performs transamination and deamination reactions to convert amino acids into intermediates for energy or synthesis.
  • Critically, the liver detoxifies ammonia through the Urea Cycle → producing urea for excretion.
  • The liver synthesizes almost all plasma proteins, including: – Albumin (maintains oncotic pressure, transports substances) – Clotting factors (II, VII, IX, X, fibrinogen) – Transport proteins (transferrin, ceruloplasmin)
  • During fasting, muscle breaks down protein → amino acids travel to the liver → converted to glucose (gluconeogenesis).
  • The liver synthesizes non-essential amino acids and modifies essential ones.

Damage to the liver → low albumin, edema, bleeding tendencies.

Lipid Metabolism in the Liver

  • The liver synthesizes fatty acids, triglycerides, cholesterol, and phospholipids.
  • Excess carbohydrates are converted to fatty acids → esterified into triglycerides → packaged into VLDL for export to tissues.
  • The liver oxidizes fatty acids via β-oxidation, especially during fasting, producing acetyl-CoA.
  • When acetyl-CoA accumulates (due to low carbohydrate availability), it is converted into ketone bodies: – Acetoacetate, β-hydroxybutyrate, and acetone. These serve as fuel for muscle and brain during fasting or starvation.
  • The liver synthesizes cholesterol, then converts some to: – Bile acids (for fat digestion), – Steroid hormones (indirectly through endocrine tissues).
  • The liver also clears lipoproteins from the blood (LDL, remnants).

If liver function or VLDL export fails → fat accumulates inside hepatocytes → fatty liver.

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