Glucose and FFA Homeostasis
In the postabsorptive (fasting) state, energy is derived primarily from the breakdown of endogenous fat stores, whereas hepatic, and, to a lesser extent, renal endogenous glucose production maintains blood glucose levels for utilization by organs such as the brain. Fatty acids derived from lipoprotein breakdown or released as FFAs from adipose tissue are oxidized as the main source of energy (Fig. 1 and Color Plate 2, following p. 34). Postprandially there is a shift toward storage of energy metabolites, mediated to a large extent by nutrient-induced insulin secretion. The postprandial rise of plasma glucose, fatty acids, amino acids, and incretin hormones stimulates the release of insulin by pancreatic [1]-cells, which serves to stimulate glucose uptake by insulin sensitive tissues such as muscle and adipose tissue and suppresses glucose production by liver and kidney (Fig. 1 and Color Plate 2, following p. 34). In addition, insulin suppresses FFA release from adipose tissue and favors their storage as TGs. Maintenance of whole-body glucose and lipid homeostasis depends upon normal insulin secretion by pancreatic [1]-cell and normal tissue sensitivity to insulin (1,2).
