Video Transcript
The diagram provided shows a basic
outline of the mechanisms of control of blood glucose. What hormones are represented by
the letters A and B, respectively?
You may recall that every cell of
the human body requires glucose for cellular respiration to release energy. We get this glucose by digesting
carbohydrates in our food using enzymes. The glucose is then absorbed into
the blood and transported all around the body. Because our energy requirements are
different at different times of the day, our blood glucose concentration must be
constantly maintained at an optimum level.
Sometimes, we will consume more
carbohydrates than are needed to match our energy requirements. When this happens, the blood
glucose concentration rises above the optimum level, as we can see on this
flowchart. The rise in blood glucose
concentration is detected by 𝛽 cells of the pancreas, which respond by releasing
insulin into the blood. Insulin is a protein hormone which
primarily acts on cells of the liver, muscles, and fat to increase their uptake of
glucose from the blood. It also promotes the conversion of
glucose into glycogen for storage. This causes the blood glucose
concentration to fall, bringing it back down to its optimum level.
On other occasions, for example, if
we are doing heavy exercise, our energy requirement will be higher than can be
provided by the carbohydrates we have consumed. In a scenario such as this, our
blood glucose concentration falls below the optimum level, as we can see here. This is also detected by the
pancreas, but this time by 𝛼 cells rather than 𝛽 cells. 𝛼 cells respond to low blood
glucose levels by releasing a different protein hormone called glucagon into the
blood. Glucagon targets cells of the
liver, causing them to convert glycogen into glucose and then to release this
glucose into the blood. As a consequence, the blood glucose
concentration rises back up to its optimum level.
We have therefore determined that
the hormones represented by the letters A and B are insulin and glucagon,
respectively.
