Blood glucose

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• After a meal there is a rise in blood glucose levels as the food in the small intestine is digested and absorbed into the bloodstream, especially if the food is high in carbohydrates.

• The glucose molecules bind to receptors in the cell membranes of small beta (β) cells in the Islets of Langerhans.

• These cells secrete the hormone insulin into the blood.

• Insulin molecules bind to receptors in the cell membranes of hepatocytes (liver cells) and other cells e.g. muscle cells.

• This increases the permeability of the hepatocyte cell membranes to glucose, so more glucose is absorbed into the liver. Decreasing the amount in the blood.

• Inside the hepatocytes, the insulin activates an enzyme that catalyses the condensation of glucose molecules into glycogen, which is stored in the cytoplasm of hepatocytes and in the muscles. This process is called glycogenesis.

• Insulin also increases the rate of respiration of glucose in other cells. The blood glucose concentration decreases.

• When there is a fall in blood glucose concentration, due to exercise or the passage of time after a meal.

• The larger alpha (α) cells of the Islets of Langerhans secrete the hormone glucagon into the blood.

• Glucagon binds to receptors on the hepatocytes.

• This activates an enzyme inside the hepatocytes that catalyses the hydrolysis of stored glycogen into glucose and is released into the blood stream. This process is called glycogenlysis.

• Liver cells also convert non-carbohydrates such as amino acids into glucose in a process called gluconeogenesis.