The levels of glucose, insulin and glucagon were measured in the plasma of 24 healthy adults at intervals over a 5-hour period - HSC - SSCE Biology - Question 31 - 2020 - Paper 1

The plasma levels measured in the first 60 minutes represent resting levels. After the meal, plasma glucose rises as a direct result of absorption of glucose from the gut into the bloodstream.

Rising blood glucose levels stimulate β cells in the pancreas to release the hormone insulin, which stimulates body cells to take up glucose to be used in their metabolism and the liver to take up glucose to be stored as glycogen. Therefore, the rise in plasma insulin in Figure 2 is a direct result of the rise in plasma glucose. As the cells and liver take up glucose, they remove the glucose from the blood leading to the subsequent fall in plasma glucose levels, hence insulin levels also fall.

Glucagon is a hormone that is an important part of the negative feedback loop that controls glucose levels in the blood. If plasma glucose falls, glucagon is released from α cells in the pancreas and causes glucose to be released from storage. This process occurs in the liver and muscles to restore normal glucose levels. In Figure 1, as glucose rises, the pancreatic cells will sense glucagon and halt glucagon release as seen in Figure 3. This will result in less glucagon being released from the liver, reducing glucose levels.