How Does Homeostasis Control Blood Glucose?
Learn how insulin and glucagon control blood glucose by negative feedback, including glycogenesis, glycogenolysis and gluconeogenesis for AQA A Level Biology.
Homeostasis controls blood glucose by negative feedback: when blood glucose rises, insulin helps lower it; when blood glucose falls, glucagon helps raise it. Negative feedback means a change triggers responses that bring a condition back towards its normal level.
This matters because cells need glucose as a substrate for respiration, while large changes in blood glucose can alter the water potential of the blood. Keeping blood glucose within limits helps maintain a suitable environment for cells. Insulin and glucagon have opposing effects, so correction works in either direction.
When blood glucose rises
After a meal, beta cells in the pancreas detect the increase and release insulin. Insulin binds to receptors on target cells. It increases glucose uptake by causing more glucose transport proteins to be added to cell membranes. It also stimulates enzymes in the liver and muscles to convert glucose into glycogen for storage. This conversion is called glycogenesis. Together, these responses reduce blood glucose.
When blood glucose falls
Between meals, alpha cells in the pancreas detect the decrease and release glucagon. Glucagon binds to receptors on liver cells and activates enzymes that break down stored glycogen into glucose. This is glycogenolysis. It also stimulates gluconeogenesis, the production of glucose from substances such as glycerol and amino acids. The liver releases glucose into the blood, raising blood glucose again.
For example, blood glucose rises after eating carbohydrates, so insulin release increases and more glucose is taken up or stored. Later, as blood glucose falls, glucagon release increases and the liver releases glucose. As the level returns towards normal, the stimulus for the corrective response decreases.
Exam mistake to avoid: do not say that glucagon directly turns glycogen into glucose or that insulin simply ‘removes’ glucose. These hormones bind to receptors and trigger responses in target cells; enzymes carry out the conversions.
