Adipose Tissue Metabolism

Adipose tissue is the major fuel storage tissue for an animal. The total stored triacylglycerols amount to some 565,000 kJ (135,000 kcal) in an average-sized human. This is enough fuel, metabolic complications aside, to sustain life for a couple of months in the absence of further caloric intake.

The adipocyte, or fat cell, is designed for continuous synthesis and breakdown of triacylglycerols, with breakdown controlled largely via the activation of hormone-sensitive lipase. Because adipocytes lack the enzyme glycerol kinase, some glucose catabolism must occur for triacylglycerol synthesis to take place--specifically, the formation of dihydroxyacetone phosphate, for reduction to glycerol-3-phosphate (see here).

Glucose acts as a sensor in adipose tissue metabolism. When glucose levels are adequate, the production of dihydroxyacetone phosphate generates enough glycerol-3-phosphate for the resynthesis of triacylglycerols from the released fatty acids. When intracellular glucose levels fall, the concentration of glycerol-3-phosphate falls also, and fatty acids are released from the adipocyte as the albumin complex for export to other tissues).

See also: Biological Fuel, Figure 23.4