Question

When an individual is in a “fight-or-flight” situation, the release of epinephrine promotes glycogen breakdown in the liver, heart, and skeletal muscle. The end product of glycogen breakdown in the liver is glucose; the end product in skeletal muscle is pyruvate (because it is immediately used by glycolytic enzymes). What is the advantage of these specific glycogen breakdown routes in the liver (glucose as final product) and skeletal muscle cells (pyruvate as final product) for an individual that must fight or flee? Explain in detail

Answer 1

Fight or flight mechanism is a body defense during stressful or life threatening conditions. During this, Muscles, heart and brain plays a major role so, blood flow is increased to these organs to supply more oxygen and glucose.

Generally excess Glucose is stored as Glycogen in liver and skeletal muscle with help of insulin. So, when body need more glucose during fight or flight, the harmone called Epinephrine is released and inhibits Insulin and activates Glucagon. Thus the increased Glucagon promotes Glycogenolysis (Glycogen break down) and releases Glucose from liver. This Glucose is used by the organs for fight or flight.

As muscles used for fight, they need energy instantly. So, Glycogenolysis directly gives the intermediates of glycolysis and helps in the energy production for muscle contraction, thus promote strength during fight. The pyruvate produced from Glycogenolysis directly enters the krebs cycle and helps in the release of high energy components (NADPH, FADH) which enters electron transport chain and releases energy (ATP) more quickly.

Thus both skeletal muscle and liver Glycogen plays a significant role in fight or flight responses.