Regulation of Metabolism

Question 1

Postprandial (Absorptive) State

Answer 1

• Occurs shortly after eating; marked by anabolism and fuel storage.
• Blood glucose rises, stimulates insulin release.
• Insulin acts at liver, muscle, adipose tissue; promotes glycogenesis in liver, then excess glucose stored as triacylglycerols; promotes glycogenesis and protein synthesis in muscle; promotes triacylglycerol synthesis in adipose tissue.
• Nervous tissue and RBCs insensitive to insulin.

Question 2

Postabsorptive (Fasting) State

Answer 2

• Glucagon stimulates glycogenolysis and gluconeogenesis in liver.
• Epinephrine stimulates release of amino acids from skeletal muscle and fatty acids from adipose tissue; amino acids and fatty acids used by liver for gluconeogenesis.

Question 3

Prolonged Fasting (Starvation)

Answer 3

• Glucagon and epinephrine levels markedly elevated during starvation.
• Results in rapid degradation of glycogen stores and gluconeogenesis in liver; rapid lipolysis results in excess acetyl-CoA used for ketone bodies synthesis; muscles start to use fatty acids as major fuel source and brain adapts to use ketones for energy.