Describe the control of blood glucose concentration by the liver and the roles of insulin and glucagon

The liver plays a crucial role in regulating blood glucose concentration, primarily through the actions of two hormones: insulin and glucagon. These hormones work in tandem to maintain glucose homeostasis, ensuring that blood sugar levels remain within a healthy range.

Role of the Liver in Glucose Regulation

The liver is central to glucose metabolism, performing several key functions:

• Glycogenesis: When blood glucose levels are high, such as after a meal, insulin is secreted by the pancreas. Insulin promotes the conversion of excess glucose into glycogen for storage in the liver. This process helps lower blood glucose levels.
• Glycogenolysis: When blood glucose levels drop (e.g., between meals or during fasting), glucagon is released by the pancreas. Glucagon stimulates the liver to convert stored glycogen back into glucose, which is then released into the bloodstream.
• Gluconeogenesis: In addition to glycogen breakdown, glucagon also promotes gluconeogenesis, which is the synthesis of glucose from non-carbohydrate sources (like amino acids and glycerol), further contributing to elevating blood glucose levels when necessary.

Insulin’s Role

Insulin, produced by beta cells in the pancreas, has several critical functions:

• Facilitating Glucose Uptake: Insulin acts on various tissues, including muscle and adipose tissue, facilitating the uptake of glucose from the bloodstream into cells where it can be used for energy.
• Inhibiting Gluconeogenesis and Glycogenolysis: Insulin suppresses the liver’s production of glucose by inhibiting gluconeogenesis and glycogenolysis. This action helps prevent excessive increases in blood sugar levels after meal.
• Promoting Storage: Insulin encourages the liver to store excess glucose as glycogen and also promotes fat storage by stimulating lipogenesis.

Glucagon’s Role

Glucagon, produced by alpha cells in the pancreas, serves as a counter-regulatory hormone to insulin:

• Raising Blood Sugar Levels: When blood sugar levels fall too low, glucagon signals the liver to release glucose into the bloodstream by stimulating glycogenolysis and gluconeogenesis.
• Response to Low Blood Sugar: Glucagon is released in response to low blood glucose levels or during periods of fasting, ensuring that the body has a continuous supply of energy, especially vital for organs like the brain.

Interaction Between Insulin and Glucagon

The interplay between insulin and glucagon exemplifies a negative feedback system that maintains blood glucose levels within a narrow range:

• High Blood Sugar: After carbohydrate-rich meals, insulin secretion increases, promoting glucose uptake and storage while suppressing hepatic glucose production.
• Low Blood Sugar: Conversely, when blood sugar levels drop, glucagon secretion rises, prompting the liver to release stored glucose back into circulation.