Video Transcript
In this video, we will learn about
the structure and function of the pituitary gland. This is a gland that plays such an
important role that it’s often called the master gland. First, we will understand the
anatomy of this endocrine gland, and then we will learn about the main hormones
released from the pituitary gland and how they affect the human body. We’ll discover how this small gland
can orchestrate almost all aspects of our lives, from our growth and metabolism to
our reproduction and even our social interactions and empathy to others.
The pituitary gland belongs to the
endocrine system, which is a series of glands in the body that secrete chemical
messengers called hormones. In addition to the pituitary gland
that sits just under the brain, some of the endocrine glands of the endocrine system
are represented in this diagram, for example, the thyroid gland, the pancreas, the
adrenal glands, and the gonads, which in biological females are the ovaries and in
biological males are the testes. They’re both represented in the
same person on this diagram even though usually only one would be found in a
person.
Hormones are released by the cells
in these endocrine glands and into the blood. Once in the blood, the hormones can
travel throughout the entire body. Eventually, they’ll reach specific
cells called target cells. Once hormones reach their target
cells or organs, they can act on these cells to cause an effect. Hormones can regulate the functions
of their target cells in order to adapt our body to our needs or to the changes in
our environment. This maintains the normal
functioning of our body. In other words, hormones contribute
to maintain homeostasis, which is the fine balance that our body maintains to make
all the body functions work in harmony.
Now let’s take a closer look at the
anatomy of the pituitary gland. As we mentioned, this gland is
located just under the brain. It’s attached to a brain region
called the hypothalamus by a stalk called the infundibulum. The gland is divided into two main
lobes: the anterior lobe, which is located closer to the front of the brain, and the
posterior lobe, which is located closer to the back of the brain. Something that may help you
remember this is that A is closer to the front of the alphabet than P. So the anterior lobe is closer to
the front of the brain than the posterior lobe.
As with many endocrine glands,
there is a rich network of blood vessels around both lobes of the pituitary gland to
collect the hormones that they release and bring them to their diverse targets
located throughout the entire body. These targets can be all sorts of
different cells and different endocrine glands. This is why the pituitary gland is
sometimes called the master gland.
Now let’s detail this anatomy a bit
more, as these two lobes are organized and function quite differently. The posterior lobe of the pituitary
gland is more a storage place for hormones that are fabricated in specialized
neurons located in the hypothalamus. The posterior lobe releases
hormones depending on neuronal signals processed in the brain by the
hypothalamus. Because this part is controlled
directly by neuron activity, it’s sometimes called the neurohypophysis.
In contrast, the anterior lobe is a
gland that contains endocrine cells. These cells produce their hormones
and release them into the bloodstream depending on signals that they received via
the blood. This part of the pituitary gland
can also be called the adenohypophysis, where the prefix adeno- means gland in
Greek.
Now let’s have a look at the
hormones released by these two lobes of the pituitary gland, starting with the
posterior lobe. This lobe secretes two hormones:
ADH, which stands for antidiuretic hormone and is also commonly known as
vasopressin, and oxytocin. ADH acts on the kidneys. As indicated by its name,
antidiuretic hormone, it acts to reduce urination. This hormone is particularly
important to maintain the water balance in our body. Its other name, vasopressin, can
help us remember that it controls our blood pressure by constricting our blood
vessels.
Oxytocin is released in high
quantities during childbirth and during breastfeeding because it stimulates uterine
contractions and also the release of milk from the mammary glands. Oxytocin also plays a very
important role in both males and females in the attachment with infants but also in
the empathetic bonds that we form with our friends, romantic partners, or even
pets. This is why oxytocin is sometimes
nicknamed the love hormone.
Now let’s have a look at the
hormones released by the anterior lobe of the pituitary gland. GH, or growth hormone, acts on many
different cells in our body, particularly our bones and muscles, to make us grow
when we are children. In adults, it still modulates our
metabolism, helping us to build muscles and strengthen our bones.
TSH, or thyroid-stimulating
hormone, acts on the cells of the thyroid gland to make them release hormones. TSH is thus called a tropic
hormone, as it acts on cells in other endocrine glands. The word tropic comes from the
Greek tropikos, which means change or turn. Indeed, tropic hormones are able to
turn on and off other endocrine glands. Tropic hormones often have the
suffix tropic or tropin in their name. For example, another name given to
TSH is thyrotropin, which in Greek means thyroid change. As we mentioned, the changes in the
thyroid gland that TSH stimulates is that it releases thyroid hormones. As a result, TSH helps us to
regulate our level of energy, body temperature, metabolism, and our blood
pressure. Thyroid hormones are also very
important for our growth and our brain development.
ACTH, or adrenocorticotropic
hormone, is a hormone that has a tropic effect too. But this time, it’s on the cortex
of the adrenal glands. ACTH is released in response to
stress and makes the adrenal glands release cortisol, a hormone that regulates our
metabolism, blood pressure, or immune responses.
The last group of hormones released
by the anterior lobe of the pituitary gland is a group of gonadatropic hormones
called gonadotropins. As indicated by the name, these
hormones have a tropic effect on the gonads. This means that they stimulate the
release of other hormones by the gonads. Remember the gonads are our sexual
glands, the ovaries in biological females and the testes in biological males. In males and females, these
gonadotropins are FSH, or follicle-stimulating hormone, and LH, or luteinizing
hormone. They are essential for the
development of the sexual organs during puberty and for the function of the
reproductive systems, especially with the production of gametes and sex
hormones.
There are two more hormones
secreted by the pituitary gland that we can mention too. Prolactin is important for the
production of milk or lactation. Lactation occurs during
breastfeeding in females. 𝛽-endorphins reduce our perception
of pain and make us feel good while exercising, listening to music, or eating
chocolate.
Let’s see how much we’ve learned
about the pituitary gland by applying our knowledge to some practice questions.
ADH and oxytocin are released by
the posterior pituitary gland. In what structure are they
produced?
This question asks us about
hormones released from the pituitary gland, which is a small gland about the size of
a pea located under the brain. The pituitary gland is divided into
two lobes according to which side of the brain they’re closest to: the anterior or
frontal part of the brain or the posterior lobe, which is located closer to the back
of the brain. Let’s take a closer look at the
pituitary gland so we can see these lobes more clearly.
The two lobes of the pituitary
gland have a different structure and they also function a bit differently. The anterior, or frontal, lobe
contains cells that produce and secrete a wide variety of hormones into the blood
that will modulate the activity of many different tissues in the body. For example, the anterior lobe
produces and releases growth hormones, or GH, that act on our muscles and bones to
stimulate our growth and metabolism.
The anterior lobe also releases
various hormones that are said to be tropic because they can stimulate the release
of other hormones by other endocrine glands, for example, ACTH that stimulates the
adrenal glands. These hormones and many others can
then be transported via the blood to their target cells.
In contrast, the posterior lobe of
the pituitary gland is not a site of production of hormones. It’s rather a site of storage of
hormones. In fact, this part contains the
terminals of specialized neurons that have the capacity to produce hormones that can
then be released into the blood. Some of the hormones that are
released from the posterior pituitary gland include ADH, or antidiuretic hormone,
and a hormone called oxytocin. The cell body of the neurons that
produce these hormones is located in a region of the brain called the
hypothalamus.
Neurons in the hypothalamus process
the information coming from the entire body and the environment, which is why the
hypothalamus is considered a control center that coordinates the nervous system and
the endocrine system. When stimulated, these neurons send
a signal along their axons and to their axon terminals to command the release of
hormones into the blood. Therefore, the answer to this
question that’s asking us where ADH and oxytocin are produced is the
hypothalamus.
Let’s try another practice question
together.
Thyrotropin in as an example of a
tropic hormone released from the pituitary gland. What is a tropic hormone? (A) A hormone that is insoluble in
the body. (B) A hormone that is transmitted
via the lymphatic system rather than the bloodstream. (C) A hormone that is only released
in response to stress. Or (D) a hormone that influences
the activity and secretions of other endocrine glands.
The pituitary gland is often
referred to as the master gland, mainly because this endocrine gland releases
hormones that target other endocrine glands in the body. We can see some of these endocrine
glands in this diagram of the endocrine system. Through their effects on other
endocrine glands, pituitary gland hormones can control the release of various other
hormones and indirectly control many more functions of the body. One example of a pituitary hormone
is thyrotropin, which you might know better as TSH, or thyroid-stimulating
hormone.
Thyrotropin stimulates the thyroid
gland to control the secretion of various thyroid hormones. In turn, these hormones regulate
many target tissues in the body. Thyrotropin in is a typical example
of a tropic hormone, which is a hormone that influences the activity and secretion
of other endocrine glands. The suffix -tropin and the
adjective tropic mean in ancient Greek to change or to turn. So if you meet the suffix in the
name of a hormone, you can guess its function.
Thyrotropin is a hormone that
changes the activity of the thyroid. Gonadotropin is a hormone that
changes the activity of the gonads. And ACTH, which is short for
adrenocorticotropic hormone, is a hormone that changes the activity of the cortex of
the adrenal glands. Therefore, we’ve worked out the
answer to our question that a tropic hormone is a hormone that influences the
activity and secretions of other endocrine glands.
Let’s summarize the key points that
we’ve learned in this video about the pituitary gland. The pituitary gland is made up of
the adenohypophysis, which is otherwise known as the anterior lobe, and the
neurohypophysis, which is otherwise known as the posterior lobe. The posterior lobe releases
hormones that are made in the hypothalamus, such as ADH and oxytocin. The anterior lobe releases tropic
hormones that affect the activity of other endocrine glands, for example, TSH, ACTH,
and gonadotropins. The anterior lobe also releases
hormones that don’t have a tropic effect but directly regulate certain cell
functions, such as growth hormone, prolactin, and 𝛽-endorphins.
