First, we need to become modestly familiar with cholesterol biosynthesis, and its connection to bile acids. Bile acids and their receptors in gut adjust cholesterol biosynthesis and the reuptake of bile acids to go back into cholesterol (fat reuse, from a distant time in our past when fat sources in diet weren't always available). Bile acids not only enable us to absorb fat soluble vitamins, but they and cholesterol also play a key role in the synthesis and metabolism of these vitamins. They have also been shown recently to play a role body wide in cellular function through the FXR and RXR gene control motifs receptors.
Cholesterol and bile acid biosynthetic pathways:
http://www.indstate.edu/thcme/mwking/cholesterol.html
Normal liver function also includes drug/xenobiotic compound detoxification, and synthesis of important vitamin cofactors, conversion of unsaturated fats to their eicosanoid (bioactive fatty acids) precursors for synthesis of both inflammatory (repair) and anti-inflammatory agents, and antioxidants that also play an important role as cellular function regulators - in adrenals, thyroids and brain.
The healthy liver is also active in glucose synthesis and energy storage as glycogen. The liver also signals for fat synthesis and storage (lipogenesis) that makes fat cells fatter. It signal for transport of stored fats to mitochondria in many cells, including muscle, for energy production as well.
More importantly for anabolic function and hypertrophy, the liver is the control center for regulation of protein synthesis. The liver also produces important signalling agents that recruit stem cells from various locations and sends them to muscle tissue, to be converted first to satellites (early myocytes) and then thru differentiation into cells that build muscle fiber.
Cholesterol, synthesized in liver, is also the building block for steroids, synthesized in adrenals and sex organs (and also other tissues, including brain). The following web page has a description of steroid hormone synthesis and its regulation.
http://www.indstate.edu/thcme/mwking/steroid-hormones.html
Cholesterol is also the building block for fat soluble vitamins. Water soluble vitamins are also synthesized in the liver and brain.
http://www.indstate.edu/thcme/mwking/vitamins.html#a
These vitamins are critical for health and proper metabolism of all cells, because these vitamins function as energy cofactors for many enzymes. Therefore, they are fundamentally important for our health, They play a crucial role in the synthesis of neurotransmitters, dopamine, serotonin, GABA and NMDA. They also regulate the synthesis of so called excitatory compounds, epinephrine, norepinephrine, aceylcholine, and glutamine.
Two of these vitamins, while considered nonessential, are absolutely vital for balanced function of many neurotransmitters and ion conduction channels in muscle, liver, lungs, brain and nerve tissues that control all organs. Taurine and its counterpart, carnitine are critical to both excitatory glutamine signal control in the brain, and also are building blocks for important antioxidants that have been shown to be important in gene regulation of thyroid hormone synthesis in thyroid, and its step wise conversion in liver and adrenals.
Glutathione and NAC also appear to play a role in thymus function, and thus control immune action, and in pituitary, playing a significant role in thyroid, adrenal and sex hormone synthesis.
Thus, cholesterol back-bone is the precursor (parent) compound for synthesis of a wide variety of highly important control agents. The liver is also the primary site of amino acid synthesis, and these are fundamental building blocks in not only proteins, but also other control agents, lipid like and water soluble, including vitamins and cofactors and neurotransmitters that regulate nervous system function.
The liver is very sensitive to upset by inappropriate sleep pattens, diet, exercise (including lack of aerobic exercise), excess stress, alcohol and drug use.
Time and again, when we see complaints of a lack of hypertrophy, difficulty in controlling fat mass when promoting hypertrophy (bulking), poor immune function, thyroid and adrenal dysfunction, difficulty sleeping, and neurological disorders - the root cause can be traced back to liver biochemistry screwups - mostly self inflicted, and ultimately, leading to chronic and debilitating disease later in life if left unattended.
Thus, your question is timely and important for members of this board.
To read about muscle biochemistry, see:
http://www.indstate.edu/thcme/mwking/muscle.html
The main Medical Biochemistry website is (that includes important discussion of cellular energetics):
http://www.indstate.edu/thcme/mwking/home.html
and I dont need anymore hair on my chest!
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