Because the liver is so important in metabolism, the term extrahepatic has been defined to mean “located or occurring outside of the liver”1. We are next going to consider extrahepatic tissue metabolism.
Figure 7.31 The liver “is kind of a big deal”2
To start considering the metabolic capabilities of the extrahepatic tissues, we start by removing pathways that only or mostly occur in the liver:
Alcohol oxidation
Gluconeogenesis
Ketone body synthesis
Urea synthesis
Lactate breakdown
Glucose-6-phosphatase
These metabolic processes are crossed off in the figure below.
Figure 7.32 Removing the pathways that only or mostly occur in the liver3
We are left with metabolic capabilities that are listed and shown below.
Glycogen synthesis and breakdown
Glycolysis
Fatty acid synthesis and breakdown
Triglyceride synthesis and breakdown
Protein synthesis and breakdown
Figure 7.33 The metabolic capability of the extrahepatic tissues3
We will use this figure as the base for metabolic capabilities of the different extrahepatic tissues to compare what pathways other tissues can perform versus all the pathways performed by extrahepatic tissues.
In an effort to keep this simple, we are going to focus on four extrahepatic tissues in the following subsections:
7.31 Muscle Macronutrient Metabolism
7.32 Adipose Macronutrient Metabolism
7.33 Brain Macronutrient Metabolism
7.34 Red Blood Cell Macronutrient Metabolism
References & Links
1. http://www.cancer.gov/dictionary/?CdrID=44498
2. http://commons.wikimedia.org/wiki/File:Liver.svg
3. http://en.wikipedia.org/wiki/File:CellRespiration.svg
