Video Transcript
Which of the following is not
promoted by the activity of insulin? (A) The uptake of glucose by cells
from the blood. (B) The production of glycogen in
cells. (C) The production of glucose
molecules by cells. Or (D) the decrease of the glucose
level in the blood if it exceeds the normal range.
This question asks us about a
hormone called insulin that is secreted by the pancreas. In order to answer this question
correctly, let’s review the key facts about the endocrine role of the pancreas and
how insulin affects blood glucose levels.
Blood glucose levels that are too
high or too low can be dangerous, but thankfully the pancreas can regulate
these. But how does it do this? The pancreas secretes two hormones:
insulin and glucagon. These are antagonistic
hormones. In other words, they work against
each other to maintain blood glucose levels within a normal range.
Let’s now look at the effects of
each hormone on the body. We will start with insulin. When blood glucose levels rise, for
example, after a meal, the pancreas detects this and responds by increasing its
secretion of insulin. The insulin is carried around the
body in the bloodstream. Most body cells have receptors for
insulin, so insulin attaches to these, which stimulates the uptake of glucose by the
cells. They then use the glucose for
cellular respiration to release energy, which they use for a variety of functions,
such as muscle contraction, production of new cellular components, and driving
metabolism.
If we look at the question, it is
asking for a process that is not stimulated by insulin. Seeming as uptake of glucose by the
cells is stimulated by insulin, we can rule out option (A).
When the insulin attaches to liver
and muscle cells, it stimulates them to take up glucose and join the molecules up to
form a complex, branched carbohydrate called glycogen. This acts as a store of glucose, as
it is insoluble and unreactive. So it just sits in the cell without
affecting the cell’s function. Insulin also causes adipose cells,
fat cells, to take up glucose and convert it into lipids for storage. We can now rule out option (B) as
the production of glycogen in cells is, again, triggered by insulin.
The removal of glucose from the
blood brings the blood glucose levels back down to within the norm, which means we
can also remove option (D) from the possible answers.
When the blood glucose levels
return to the norm, it is detected by the pancreas, and insulin secretion is
reduced. Insulin also suppresses the release
of the hormone glucagon so that it is not secreted when blood sugar levels are
normal or above normal. However, when blood glucose levels
drop, it is the glucagon’s turn to do its work. When blood glucose levels drop, it
is, again, detected by the pancreas. This time it is glucagon that is
released into the blood as a response. Glucagon is carried around the body
and binds to receptors on the liver, causing the breakdown of the stored glycogen
into single glucose molecules. Glucagon also triggers the liver
cells to make glucose from amino acids and glycerol. The glucose is then released into
the blood, helping to bring the blood glucose concentration back up to the norm.
We can now return to our question,
which asks us which of the responses is not promoted by the activity of insulin. As we reviewed the key points about
the pancreas and its hormones, we ruled out options (A), (B), and (D), as these are
all processes stimulated by the release of insulin. We are therefore left with the
correct answer (C). The response that is not promoted
by the activity of insulin is the production of glucose molecules by cells.
