Liver glucose metabolism

Lipid metabolism in the liver is closely linked to the carbohydrate and amino acid metabolism. When there is a good supply of nutrients in the resorptive (wellfed) state (see p. 308), the liver converts glucose via acetyl CoA into fatty acids. The liver can also take up fatty acids from chylomicrons, which are supplied by the intestine, or from fatty acid-albumin complexes (see p. 162). Fatty acids from both sources are converted into fats and phospholipids. Together with apoproteins, they are packed into very-low-density lipoproteins (VLDLs see p.278) and then released into the blood by exocytosis. The VLDLs supply extrahepatic tissue, particularly adipose tissue and muscle. 

Some mammalian cells have the ability to metabolize glucose 6-phosphate in a pathway that involves the production of C3, C4, C5, C6, and C7 sugars. This process also yields the reduced coenzyme, NADPH, which is oxidized in the biosynthesis of fatty acids and steroids (Chap. 13). Consequently, this metabolic pathway is of major importance in those cells involved in fatty acid and steroid production, such as the liver, lactating mammary gland, adrenal cortex, and adipose tissue. The pentose phosphate pathway, which does not require oxygen and which occurs in the cytoplasm of these cells, has two other names the phosphogluconate pathway (after the first product in the pathway) and the hexose monophosphate shunt (since the end products of the pathway can reenter glycolysis). 

Chromium Altered glucose metabolism Glucose intolerance and malnutrition Liver and kidney impairment Dermatitis Convulsions and coma Respiratory tract and lung cancers (Cr(VI))... 

The development of liver X receptor agonists has been an area of interest for over a decade, given the critical role of those receptors in cholesterol metabolism, glucose homeostasis, inflammation, innate immunity, and lipogenesis. Potential indications include atherosclerosis, diabetes, inflammation, AD, and cancer [442, 443],... 

The liver and kidney, which do not metabolize glucose to a significant degree, rely primarily on fatty acid... 

Explain the changes in liver metabolism that occur when blood glucose levels drop after a meal has been digested. 

In both muscle and liver cells, glucose 1-phosphate produced from glycogen is converted to glucose 6-phosphate. In muscle cells, this metabolite enters the glycolytic pathway and is metabolized to generate ATP for use in powering muscle contraction (Chapter 8). Unlike muscle cells, liver cells... 

Fig. 31.15. Glucose metabolism in various tissues. A. Effect of insulin on glycogen synthesis and degradation and on VLDL synthesis in the liver. B. Glucose metabolism in resting muscle in the fed state. The transport of glucose into cells and the synthesis of glycogen are stimulated by insulin. C. Glucose metabolism in adipose tissue in the fed state. FA = fatty acids DHAP = dihydroxyacetone phosphate. FA = fatty acids TG = triacylglycerols -I- = stimulated by insulin — = inhibited by insulin.

---