Glucagon is another hormone produced by the pancreas.
Question: Can you recall which cells make glucagon?
It is produced by the α (alpha) cells of the islets of Langerhans in the pancreas (see Figure 2).
Glucagon causes an increase in the blood glucose level. The glucagon level in the blood tends to decrease as the glucose level increases and increases when the level of glucose decreases. It works in the opposite direction to insulin. It stimulates the liver to break down glycogen (the molecule synthesised from glucose that acts as a glucose store) and release glucose into the blood.
You may wonder why the body needs a hormone to increase glucose levels. Besides having to avoid circumstances where blood glucose is too high, the body also needs to be protected from glucose levels that are too low, as the brain does not function properly in these circumstances, as you saw earlier. There are lots of hormones that increase glucose levels by stimulating glycolysis, and glucagon is one of the most important.
You have been reading about some very complex processes in the body. Try Activity 3 to see if your knowledge of the processes involved in diabetes has increased.
Activity 3: The effect of drinking a sugary drink – revisited
Make brief notes on the effect that a drink containing a lot of glucose or digestible sugar might have on blood glucose level, in:
(a) someone with diabetes; and
(b) someone without diabetes.
How has your answer differed from that to Activity 2? In someone without diabetes, the blood glucose level goes up quickly and then starts to decrease, staying within normal limits. A person with some insulin but not enough, who drinks a sugary drink, will find their blood glucose level goes above the normal limits. (Blood glucose levels can reach 20 mmol/l or more after a sugary drink.) The blood glucose level comes down much more slowly in people with diabetes than in people who have a normal amount of insulin. The level to which it falls after a sugary drink depends on how much insulin is present. If there is no insulin available at all, the blood glucose level remains very high.