Control of Blood Glucose Concentration (AQA A Level Biology)

The Role of the Liver in the Conversion Between Glycogen & Glucose

• The liver plays a vital role in the conversion between glycogen and glucose

  • The conversion between these molecules helps to regulate blood glucose concentration

• Both insulin and glucagon have specific receptors on the membranes of liver cells

• When these hormones bind to their receptors they trigger several processes within the liver

  • Glycogenesis

  • Glycogenolysis

  • Gluconeogenesis

Glycogenesis

• Glycgogenesis is the synthesis of glycogen from glucose molecules

• Insulin triggers this process after it detects an increased blood glucose concentration

• The synthesis of glycogen removes glucose molecules from the bloodstream and decreases the blood glucose concentration to within a normal range

• Glycogen acts as a compact and efficient carbohydrate storage molecule

Glycogenolysis

• Glycogenolysis is the breakdown of glycogen to produce glucose molecules

• Glucagon triggers this process after it detects a decreased blood glucose concentration

• It activates enzymes within the liver that breakdown glycogen molecules into glucose

• The breakdown of glycogen releases more glucose molecules to the bloodstream and increases the blood glucose concentration to within the normal range

Gluconeogenesis

• Gluconeogenesis is the synthesis of glucose molecules from non-carbohydrate molecules

• Glucagon also triggers this by activating enzymes within the liver

• These enzymes convert other molecules, such as fatty acids and amino acids, into glucose molecules

• Glucose molecules are released into the bloodstream which increases the blood glucose concentration to within the normal range

Blood Glucose Concentration

• There are three ways in which glucose can enter the bloodstream:

  • Absorption in the gut following carbohydrate digestion

  • Hydrolysis of glycogen stores

  • Non-carbohydrates such as lipids, lactate and amino acids that have been converted to glucose

• The amount of glucose that gets absorbed into the blood from the products of digestion can vary substantially

  • Some meals may be much more carbohydrate-rich than others

• Control systems within the body help to manage the concentration of glucose in the blood via the hormones insulin and glucagon

• When there is excess glucose in the blood from a carbohydrate-dense meal it is removed

  • This occurs through increased glucose uptake into muscle, fat and liver cells and glycogenesis

• When there is insufficient glucose in the blood for metabolic needs it is rapidly released from storage molecules

  • This occurs through glycogenolysis and gluconeogenesis

• The levels of insulin and glucagon present in the blood are constantly regulated and adjusted in order to maintain the blood glucose concentration at a mostly constant level