Video Transcript
Which of the following is not one
of the primary functions of thyroxine in the human body? (A) Stimulating mental and physical
growth. (B) Maintaining normal body
temperature. (C) Increasing the amount of
calcium in the bloodstream. (D) Maintaining a normal heart
rate. Or (E) regulating the basal
metabolic rate.
Thyroxine, which is sometimes known
as T4, is the main hormone that’s secreted from the thyroid gland in the human
body. And it plays many important
functions in the body. In this question, we are being
asked to identify which function that’s listed below is not one of the functions of
thyroxine. Let’s work through the options to
find the correct answer.
Thyroxine does play a crucial role
in stimulating brain development and brain function. It’s responsible for developing the
brain in the embryonic stage and also for physical growth. We’ve therefore deduced that
stimulating mental and physical growth is one of the main functions of
thyroxine. So we can eliminate this
option.
Thyroxine also plays an important
role in our metabolism. Metabolism describes all the
chemical reactions that occur within the body to maintain life, including those that
release energy for our cells to use. By regulating the amount of energy
available in the body, thyroxine helps to maintain a normal body temperature. So we can eliminate this option
too. Through its regulation of
metabolism, thyroxine also helps to regulate the heart rate. So this option cannot be our
correct answer.
The basal metabolic rate is the
rate at which the body uses energy while at rest to perform crucial body
functions. By enhancing the rate of cellular
respiration and the uptake of glucose in cells, thyroxine can increase the basal
metabolic rate. If glucose needs to be delivered to
the cells faster, the rate of the heartbeat that pumps blood containing glucose to
all the body cells will also need to be maintained. This is why thyroxine does not only
regulate the basal metabolic rate, but it also regulates the heart rate. So we’ve deduced that this option
will also be incorrect.
On the posterior surface of the
thyroid gland, there are four glands called parathyroid glands, which secrete a
hormone called parathyroid hormone, or PTH for short. Parathyroid hormone, not thyroxine,
is responsible for increasing the amount of calcium in the bloodstream to maintain
the level of calcium in the blood. This means that this is not a
function of the thyroid gland, but of the parathyroid gland hormones. And so the incorrect function of
thyroxine is therefore increasing the amount of calcium in the bloodstream.
