7.2: Liver Macronutrient and Alcohol Metabolism

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The liver is the organ that has the greatest macronutrient metabolic capability; there are a number of metabolic functions that only the liver performs. However, there are two major macronutrient metabolic processes, lactate synthesis and ketone body breakdown, that the liver will not normally perform, as shown in the figure below.

Figure \(\PageIndex{1}\): Ketone body breakdown and lactate synthesis are major macronutrient metabolic pathways that the liver does not normally perform1

But aside from those two pathways, the liver performs all the other metabolic pathways that you have learned about that are listed and shown below:

Glycogen synthesis and breakdown
Glycolysis
Gluconeogenesis
Alcohol oxidation
Ketone body synthesis
Fatty acid synthesis and breakdown
Triglyceride synthesis and breakdown
Protein synthesis and breakdown
Urea synthesis
VLDL synthesis
Glucose-6-phosphatase

Figure \(\PageIndex{2}\): Metabolic capability of the liver1

The liver is the only tissue that performs the following functions:

Ketone body synthesis
Urea synthesis
VLDL synthesis

The liver is also the primary, but not exclusive site, of the following functions:

Alcohol oxidation (also occurs in the stomach)
Gluconeogenesis (also occurs in the kidney(s))
Glucose-6-phosphatase activity (also occurs in the kidney(s))
Lactate breakdown (also occurs in muscle)2

Glucose-6-phosphatase is important because it removes the phosphate from glucose-6-phosphate so that glucose can be released into circulation. Kidneys have glucose-6-phosphatase and can perform gluconeogenesis. However, it is estimated that 90% of glucose formed from gluconeogenesis is produced by the liver; the remaining 10% is produced by the kidney(s). It is also important to note that the muscle does not have this enzyme, so it cannot release glucose into circulation3.

ADAPT \(\PageIndex{1}\)

ADAPT \(\PageIndex{2}\)

References

en.Wikipedia.org/wiki/File:CellRespiration.svg
Phypers B, Pierce JMT. (2006) Lactate physiology in health and disease. Continuing Education in Anaesthesia Critical Care & Pain, 6(3).
Stipanuk MH. (2006) Biochemical, physiological, & molecular aspects of human nutrition. St. Louis, MO: Saunders Elsevier.