Glucagon

Definition

Glucagon is a peptide hormone produced by the alpha cells of the pancreas that plays a critical role in glucose metabolism by increasing blood glucose levels. It is primarily released during fasting states when blood glucose levels are low, signaling the liver to convert glycogen into glucose and release it into the bloodstream, thus ensuring a continuous supply of energy for the body.

5 Must Know Facts For Your Next Test

1. Glucagon secretion is triggered by low blood sugar levels, stress, and certain amino acids, particularly during fasting or intense exercise.
2. In addition to promoting glycogenolysis in the liver, glucagon also stimulates gluconeogenesis, the production of glucose from non-carbohydrate sources.
3. Glucagon has an opposite effect to insulin, as it raises blood glucose levels while insulin lowers them, demonstrating a key regulatory mechanism in metabolism.
4. The action of glucagon is mediated through specific receptors on target cells that activate intracellular signaling pathways to mobilize energy stores.
5. Excessive glucagon can lead to hyperglycemia and potentially contribute to conditions like diabetes if not properly regulated.

Review Questions

• How does glucagon function during fasting states to maintain blood glucose levels?
  • During fasting states, when blood glucose levels drop, glucagon is secreted by the alpha cells of the pancreas. It acts primarily on the liver to promote glycogenolysis and gluconeogenesis. This process converts stored glycogen back into glucose and creates new glucose from non-carbohydrate sources. The release of glucose into the bloodstream helps maintain adequate energy supplies for vital functions.
• Compare and contrast the roles of glucagon and insulin in regulating blood glucose homeostasis.
  • Glucagon and insulin have opposing roles in maintaining blood glucose homeostasis. While glucagon raises blood glucose levels by stimulating glycogen breakdown and glucose production in the liver during fasting states, insulin lowers blood glucose levels by promoting glucose uptake into cells and facilitating glycogen storage after meals. The balance between these two hormones is crucial for energy regulation, ensuring that blood sugar levels remain within a healthy range.
• Evaluate how glucagon's mechanisms of action integrate with metabolic responses in different tissues during exercise.
  • During exercise, glucagon plays a significant role in mobilizing energy reserves. As physical activity increases energy demand, glucagon secretion rises to elevate blood glucose levels. It stimulates glycogenolysis in the liver and encourages fatty acid release from adipose tissue for oxidation. This integration ensures that muscles receive a steady supply of glucose and fatty acids for sustained performance. The coordination between glucagon's actions and metabolic adaptations in different tissues highlights its importance in supporting energy requirements during varying physical conditions.

Related terms

Insulin: A hormone produced by the beta cells of the pancreas that lowers blood glucose levels by promoting the uptake of glucose by cells and stimulating glycogen synthesis in the liver.

Glycogenolysis: The biochemical process of breaking down glycogen into glucose-1-phosphate, which is then converted to glucose, primarily occurring in the liver.

Liver Metabolism: The series of biochemical processes that occur in the liver, including gluconeogenesis, glycogen synthesis and breakdown, and lipid metabolism, which are crucial for maintaining energy homeostasis.