Video Transcript
Which label on this diagram of the
human body indicates the thyroid gland?
This question asks us to identify
the thyroid gland in our diagram. To answer this, let’s review some
key facts about the organ system represented by this diagram. This diagram shows the endocrine
system. The endocrine system is composed of
many different organs with functions that may seem unrelated at first. For instance, some of these organs
influence reproduction, while others aid in digestion. Some are even responsible for
systemic effects like the regulation of metabolism, growth, and blood pressure. So, what do these organs have in
common?
Glands of the endocrine system
release hormones usually into the bloodstream. These hormones are chemical
messengers that are carried around the body to their target cells to bring about a
response. The pituitary gland, shown at the
top of the diagram, just below the brain, is considered the master gland of the
endocrine system. This is because it releases seven
different hormones that influence other organs of the endocrine system, including
the thyroid gland, adrenal glands, ovaries, and testes. For instance, the pituitary gland
releases follicle-stimulating hormone, or FSH. This hormone is not only essential
for development during puberty but also for control of the menstrual cycle and sperm
production.
Another hormone released from the
pituitary gland is thyroid-stimulating hormone, or TSH. So what organ does
thyroid-stimulating hormone influence? You may have guessed the thyroid
gland, as the clue was in the name. The thyroid gland is a
butterfly-shaped endocrine gland, located at the base of your neck. It is made up of two types of
secretory cells, follicular cells and parafollicular cells, as shown here. The follicular cells secrete the
thyroid hormones thyroxine and triiodothyronine, which regulate the basal metabolic
rate of the body. They are also involved in the
control of heart rate, digestion, muscle control, and brain function.
The parafollicular cells secrete
calcitonin. This hormone works with parathyroid
hormone, which is secreted by the parathyroid glands to regulate blood calcium
levels. When calcium levels rise above
normal, calcitonin is released by the thyroid gland to bring the levels back
down. When calcium levels in the blood
drop below normal, parathyroid hormone is released to bring them back up.
It is the thyroid gland we have
been asked to locate in this question, so let’s take another look at our diagram and
review the structures marked by X, Y, and Z. Label X points to a structure in
the brain that sits right above the pituitary gland, and this is the
hypothalamus. While the pituitary gland is
considered the master gland in the endocrine system, its secretions are actually
regulated by the hypothalamus. Because the hypothalamus is part of
the brain and the pituitary gland controls much of the endocrine system, the
hypothalamus links the nervous and endocrine systems together.
Now let’s have a look at label
Y. This is pointing to a gland that
actually serves both the endocrine and digestive system. This organ is called the
pancreas. And it is responsible for secreting
the hormones insulin and glucagon from an area called the islets of Langerhans. These hormones are very important
for regulating blood glucose levels. As well as secretion of hormones,
it secretes digestive enzymes from the acinar cells and releases them down ducts
into the duodenum.
This leaves us with letter Z. You can see it is a butterfly shape
and found in the neck, which means we have already mentioned this gland, the thyroid
gland. We can now answer this question
correctly. We are asked which label on this
diagram of the human body indicates the thyroid gland. And the correct label is Z.
