Video Transcript
The concentration of glucose in the
bloodstream needs to be carefully controlled. Otherwise, there can be serious
effects on the body. Which of the following is not one
of these effects? (A) High blood sugar, damaging
blood vessels. (B) High blood sugar, damaging
organs. (C) Low blood sugar, resulting in
fainting. Or (D) low blood sugar, resulting
in excessive energy.
This question presents us with some
complications arising from blood glucose levels that are either too high or too
low. Have you heard of the organ that
secretes hormones to regulate blood glucose levels? It is the pancreas, which secretes
glucagon and insulin. To answer our question, let’s
briefly discuss this organ and the issues that arise when blood glucose strays from
the optimum levels.
Blood glucose concentration is
controlled by a negative feedback mechanism. When blood glucose levels rise,
such as after a meal, the pancreas detects this and responds by secreting insulin
into the blood. Most body cells have receptors for
insulin on their cell membrane. As the insulin is carried around
the body, it attaches to these receptors, promoting the uptake of glucose by the
cells, which is then used in cellular respiration to release energy. When the insulin reaches cells of
the liver and muscle, it attaches to their receptors, stimulating them to take up
glucose and convert it into the complex carbohydrate glycogen.
Glycogen is made up of thousands of
connected glucose molecules. It is a suitable storage
carbohydrate as it is unreactive and almost insoluble so can sit inside the cell
without disrupting it. Insulin also triggers the adipose,
fat, cells to take up glucose and convert it into lipid stores. The removal of the glucose from the
blood brings the blood glucose levels back down to the norm.
The release of insulin suppresses
the release of glucagon. But as glucose levels return to the
norm, insulin secretion drops. This means that when blood glucose
concentration falls, such as after exercise, glucagon can be released into the blood
by the pancreas. The glucagon attaches to receptors
on the liver cells, causing them to break down their glycogen stores, releasing
glucose, which then enters the blood. It also stimulates the liver cells
to make new glucose molecules out of amino acids and glycerol, which further
increases the blood glucose concentration. Therefore, blood glucose rises back
up to the norm. The muscle cells are not involved
in this second response as they will use up their stores themselves to release
energy for muscle contraction.
Let’s now look at what happens if
the blood concentration is not controlled, for example, if a person has type one
diabetes. Type one diabetes is an autoimmune
disease that attacks the pancreas, so it produces little or no insulin. A person with this disease needs to
control their blood glucose with insulin injections or pumps. Without insulin, these patients’
blood glucose levels will rise too high after food, as the muscle cells and liver
cells will not be taking the glucose up and storing it as glycogen. This condition is known as
hyperglycemia, hyper- meaning high and “glycemia” referring to glucose, and it
causes several complications.
One such complication is an
increase in blood pressure due to various factors, such as the blood vessels losing
their stretch and an increase in body fluid. High blood pressure will put
increased stress on organs and tissues, which can damage them. Seeming as the question is asking
for an effect not caused by an imbalance of blood glucose and options (A) and (B)
are serious effects, we can rule these out.
We have so far looked at what
happens if the blood glucose concentration rises. So now let’s look at what happens
when the blood glucose drops too low. If somebody with type one diabetes
did not have injections of insulin, then the excess glucose after a meal will not be
able to be taken up and stored. It will be excreted in urine. This can lead to hypoglycemia,
hypo- meaning low, as no stores of glycogen means that there is no glucose to be
released into the blood. This is a real problem as glucose
is needed for respiration to release energy for the body to use.
Hypoglycemia also reduces blood
pressure, partly because blood is being diverted to the brain, as brain cells
usually only respire glucose, and also to the heart to keep it contracting. Both the lack of glucose and the
low blood pressure lead to various telltale symptoms of hypoglycemia and so too type
one diabetes. These include tiredness, feeling
sick, sweating, confusion, fainting, seizures, coma, and even death if not treated
in time. So low blood sugar resulting in
fainting is a serious effect of unbalanced blood glucose concentrations, which means
that (C) is not the correct answer to the question.
Now that we have reviewed some
effects that irregular blood glucose levels can have on the body, we can return to
our question. Having ruled out all the other
options, we are left with the correct answer, which is option (D). The choice that does not give a
serious effect caused if concentration of glucose in the bloodstream is not
carefully controlled is low blood sugar, resulting in excessive energy.
