Metabolic homeostasis

Glial cells are cells within the central or peripheral nervous system which are not immediately involved in information processing. Glial cells play an mportant role in the metabolic homeostasis of brain tissue and in nervous system development. 

It has been estimated that there are several billion neurons that comprise the mammalian brain which, together with their surrounding glial cells, form a unique network of connections which are ultimately responsible for aU thoughts and actions. While the glial cells may play a critical role in brain development, their main function in the mature brain is to maintain the structure and metabolic homeostasis of the neurons which they surround. 

In the absence of definitive human data, risk assessment may have to depend on the results of cancer bioassays in laboratory animals, short-term tests, or other experimental methods. Hence the following issues must be addressed under such circumstances the ability of the test system to predict risks for man (quantitatively as well as qualitatively) the reproducibility of test results the influence of species differences in pharmacokinetics, metabolism, homeostasis, repair rates, life span, organ sensitivity, and baseline cancer rates extrapolation across dose and dose rates, and routes of exposure the significance of benign tumors fitting models to the data in order to characterize dose-incidence relationships and the significance of negative results. 

As with every aspect of metabolism, homeostasis is essential to the immune system, which must be able to both grow and shrink rapidly.3733 Antigens, cytokines, apoptosis-inducing signals, immune inhibitor receptors,22913 and receptor tyrosine kinases373d all participate in preserving the delicate balance that is required. 

The gut microbiome is also being investigated for its role in severe malnutrition states such as kwashiorkor (156,157). Indeed, a complex interplay exists between the gut microbiota and host metabolism, and likely has far-ranging implications on normal metabolic homeostasis as well as several disease states, the mechanisms of which we are just beginning to elucidate. 

Hochachka, P.W. and G.B. McClelland (1997). Cellular metabolic homeostasis during large scale changes in ATP turnover rates in muscles. J. Exp. Biol. 200 381-386. 

In summary, HMG-CoA lyase deficiency is a unique inborn error of metabolism with profound effects on both amino acid catabolism and metabolic homeostasis in the fasted state. Management of these patients is difficult and requires constant attention to daily nutrition and timely intervention during acute illness. Fortunately, nutritional therapy treatment that provides a diet adequate for growth but with limited intake of leucine and prevents fasting and hypoglycemia enables individuals with HMG-CoA lyase deficiency to live normal active lives. 

Thus, metabolic homeostasis of the glutamate/glutamine system may be a fertile avenue to pursue in order to identify novel targets for pharmacotherapy directed at a number of diseases of the brain. 

R.G. Shulman and D.L. Rothman. 1996. Enzymatic phosphorylation of muscle glycogen synthase A mechanism for maintenance of metabolic homeostasis Proc. Natl. Acad. Sci. USA 93 7491-7495. (PubMed) (Full Text in PMC)... 

The plasma lipoproteins play a central role in metabolic homeostasis. As discussed in Chapter 20, a lipoprotein is a complex composed of triacylglycerol, protein, cholesterol (free or esterified), and phospholipids. The phospholipid and protein form an external coat to render the particles soluble in plasma for transport around the body. The roles of lipoproteins in metabolic homeostasis are presented in Chapter 20. 

The endocrine pancreas is pivotal in metabolic homeostasis and an integral component of metabolic regulation (see also Chapter 30). It is composed of 1-2 million islets of Langerhans scattered throughout the organ and forming... 

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