• Elevated concentrations of glucose in blood stimulate release of insulin, and insulin acts on cells thoughout the body to stimulate uptake, utilization and storage of glucose.
• The effects of insulin on glucose metabolism vary depending on the target tissue.

• Insulin facilitates entry of glucose into muscle, adipose and several other tissues. In the absense of insulin, the glucose transporters are present in cytoplasmic vesicles, where they useless for transporting glucose. Binding of insulin to receptors on such cells leads rapidly to fusion of those vesicles with the plasma membrane and insertion of the glucose transporters, thereby giving the cell an ability to efficiently take up glucose.

• Insulin stimulates the liver to store glucose in the form of glycogen. A large fraction of glucose absorbed from the small intestine is immediately taken up by hepatocytes, which convert it into the storage polymer glycogen.

• Activates hexokinase - phosphorylates glucose, trapping it within the cell;

• Inhibits the activity of glucose-6-phosphatase - reducing transforamtion of glucose-6-phopahte back into glucose.

• Activates several of the enzymes that are directly involved in glycogen synthesis, including phosphofructokinase and glycogen synthase.

Insulin and Lipid Metabolism

• Insulin has a fat-sparing effect.

• Promotes synthesis of fatty acids in the liver.

• Inhibits breakdown of fat in adipose tissue by inhibiting the intracellular lipase that hydrolyzes triglycerides to release fatty acids.

• Stimulates the uptake of amino acids, again contributing to its overall anabolic effect.

• Insulin also increases the permiability of many cells to potassium, magnesium and phosphate ions.