AQA A Level Biology复习笔记6.4.6 Control of Blood Glucose Concentration

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

Exam Tip

You may be asked to define the processes above in an exam. Remember that processes with "gen" in their name usually means something has been created or synthesised. Processes with "lysis" in their name usually means something has been broken down.

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

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