D3.3 Homeostasis

Blood glucose has risen above the set point of 4.0–7.0 mmol/L after a carbohydrate-rich meal. The body must lower it back to normal — this is a classic negative feedback scenario.

Beta (β) cells in the islets of Langerhans detect elevated blood glucose. They respond by secreting insulin directly into the bloodstream.

Insulin stimulates body cells (especially liver and muscle) to take up glucose and convert it to glycogen via glycogenesis. This removes glucose from the blood, lowering the concentration back toward the set point.

The correct answer is: Beta cells of the pancreatic islets secrete insulin, promoting glycogen synthesis in the liver and muscle. This precisely matches the homeostatic response to high blood glucose.

We need the mechanism that lowers blood glucose after a meal — i.e., the response to hyperglycaemia.

Glucagon is secreted by alpha cells and raises blood glucose by breaking down glycogen. This would worsen high blood glucose — eliminate this option.

Healthy kidneys do not excrete glucose in urine — reabsorption returns glucose to the blood. Glucose appears in urine only in uncontrolled diabetes. Eliminate.

Adrenaline is a stress hormone that typically raises blood glucose by promoting glycogenolysis. It does not direct excess glucose into fat as a homeostatic glucose-lowering response. Eliminate.

The only physiologically accurate response to elevated blood glucose is: Beta cells secrete insulin → glycogen synthesis → blood glucose falls. This is the correct answer.

Blood glucose has fallen below the normal range of 4.0–7.0 mmol/L during fasting. The body needs to raise it back to the set point.

Alpha (α) cells in the islets of Langerhans detect low blood glucose and secrete glucagon — not insulin. Remember: alpha = glucagon, beta = insulin.

Glucagon travels to the liver and promotes glycogenolysis — the breakdown of stored glycogen into glucose. This releases glucose into the blood, raising the concentration back toward the set point.

The correct row is: Alpha cells → Glucagon → Glycogenolysis in the liver. This is the standard negative feedback response to hypoglycaemia.

We need the row where all three components — sensing cell, hormone, and liver action — correctly describe the response to low blood glucose.

Insulin is released in response to high glucose, and glycogenesis stores glucose as glycogen. Both actions would further lower blood glucose — wrong direction. Eliminate.

Glucagon is secreted by alpha cells, not beta cells. This row has the wrong sensing cell paired with glucagon. Eliminate.

Alpha cells do not secrete insulin — that is the role of beta cells. The hormone is also incorrect for raising blood glucose. Eliminate.

Only Alpha cells → Glucagon → Glycogenolysis correctly describes all three components of the response to low blood glucose.