Video Transcript
In this video, we are going to
explore the effects of different hormones produced by the various endocrine glands
of our body. We will outline the pituitary gland
located under the brain which is often called the master gland because of the
control it has on other endocrine glands. We will also see how other
endocrine glands play many diverse roles in our bodies controlling our reproduction,
growth, metabolism, responses to danger, and even our emotions. We will understand how all these
glands play that part so that our body maintains a constant and healthy state
despite all of the changes going on within us and around us.
Hormones are chemical messengers
that are produced by the cells in endocrine glands and are secreted into the
bloodstream. In the blood, these hormones can
travel around the entire body. Eventually hormones will reach
their target cells, upon which the hormones can cause a specific effect. In humans, the main endocrine
glands include the pituitary gland, the thyroid gland, the pancreas, the adrenal
glands, and the gonads. The gonads in biological females
are the ovaries, while the gonads in biological males are the testes. However, on this diagram, we’ve
shown both.
As we mentioned earlier once
hormones reach their target cells, they can induce different responses. For example, they can regulate
cellular functions to aim to adapt our body to changes occurring in our internal and
the external environment. An example of an internal change in
the environment might be eating sugar, or a change in our external environment could
be when facing a sudden danger. The responses to these changes aim
to maintain the normal functioning of the body. As a result, we usually say that
hormones contribute to homeostasis, which is our body’s capacity to maintain
constant conditions despite all the changes going on within us and around us.
Now, let’s take a tour of the major
endocrine glands in the body, starting with the pituitary gland. This gland is quite small, about
the size of a pea. It’s divided into two lobes and is
located just under the brain. Even though the pituitary gland is
one of the smallest glands in our body, it is sometimes called the master gland
because some pituitary hormones can control many other endocrine glands, for
example, the thyroid gland.
Let’s look at an example of a
hormone produced by the pituitary gland that has an effect on the thyroid gland. This hormone is called
thyroid-stimulating hormone or TSH. And it’s secreted into the blood
vessels that surround the pituitary gland. As is suggested by its name,
thyroid-stimulating hormone can then travel via the bloodstream to the thyroid
gland. When TSH reaches the thyroid gland,
which is located in the front base of the neck, it instructs specific thyroid cells
to produce and secrete another hormone called thyroxine. Thyroxine can then travel via the
bloodstream to have an effect on various target cells. For example, thyroxine can modulate
our energy level, our metabolism, our growth, and even our brain, heart, muscle, and
digestive system function.
Another hormone that’s produced by
the thyroid gland is called calcitonin. This hormone is not controlled by
the pituitary gland but by the level of calcium in the blood, as indicated by its
name calcitonin. Calcium is the most abundant
mineral in our body. As you might know, it’s very
important to build our bones but also for our muscles to contract and for our
nervous system to function properly. Calcitonin helps to maintain an
adequate level of calcium in our bloodstream. The pituitary gland also releases
hormones that have a direct effect on many types of cells in the body. One example is growth hormone or
GH.
GH acts primarily on our bone and
on our muscle cells, determining their development and growth. This is the hormone that helps
determine how tall you are. Without enough growth hormone,
dwarfism may occur, causing the height of some people to remain under 120
centimeters. By contrast to GH which has so many
effects on various cell types in the body, some hormones released by the pituitary
gland can have an effect on just one specific organ of our body. That’s the case with antidiuretic
hormone often known as ADH, which acts primarily on the kidneys to prevent them from
eliminating too much water. For example, if you’re stuck in a
hot desert without much to drink, your body needs to be very savvy with the water
that it contains. The action of ADH can be vital in
these situations to retain more water within the bloodstream.
The other lobe of the pituitary
gland secretes a hormone that should not be confused with ADH. This hormone is called
adrenocorticotropic hormone or ACTH for short. ACTH changes the activity of the
endocrine glands that are located just on top of each kidney which are called the
adrenal glands. Under the activation of ACTH, the
adrenal glands release another hormone. This hormone is called cortisol,
and it’s very important to mediate our response to stress. Sometimes, stress can be very
sudden, for example, when we are surprised by a storm with lightning and
thunder. In this case, our body needs to
react fast to this acute stress or immediate danger.
In these cases, the adrenal glands
secrete another hormone called adrenaline. This hormone makes us react faster
than cortisol and triggers what we call a fight-or-flight response. In this type of response,
adrenaline activates many of our body functions such as increasing the blood flow to
our muscles, increasing heart rate, and dilating the bronchioles in the lungs among
others that help us to escape or fight through a dangerous situation. A pituitary hormone that’s worth
mentioning is oxytocin. Oxytocin is involved in childbirth
by inducing contractions of the uterus. Oxytocin also plays a role in milk
ejection. Prolactin, another pituitary
hormone, stimulates milk production in a biological female’s mammary glands, usually
around the midpoint of pregnancy. Oxytocin induces this milk ejection
from the mammary glands.
Oxytocin also has important effects
on the brain. It’s an important influencer of
social bonding and emotional responses, such as trust, empathy, and positive
communication. That’s why it’s sometimes called
the love hormone. The pituitary gland also secretes
hormones called gonadotropins. As indicated by their name,
gonadotropins control the activity of the gonads. The gonads are our sexual glands
that produce the gametes for our reproduction and a series of sex hormones. In biological females, the gonads
are the ovaries, while in biological males, the gonads are the testes. Let’s see how these hormones
work.
The reaction starts at a time
called puberty. This is a period of maturation
during which our body acquires its adult features. During this time, our body goes
through lots of changes developing various secondary sexual characteristics. For example, under the effect of
testosterone, which is released from the males testes, biological males tend to
develop more muscle mass and experience increased growth of facial and body
hair. Under the effect of estrogen that’s
produced in the ovaries of biological females, however, breasts tend to develop, in
addition to the widening of the hips and various other physical characteristics.
Puberty in biological females is
also when the menstrual cycle begins, which means that during this cycle an egg is
released from the ovaries during ovulation. In parallel, the lining of the
uterus builds up to prepare for a possible pregnancy. Progesterone is a hormone that’s
secreted from the ovaries to thicken the lining of the uterus which is also called
the endometrium. If there is no pregnancy, this
lining shades away during menstruation which is sometimes called a period, and then
a new menstrual cycle can start. Thanks to the pituitary gland,
we’ve been able to review most of the main endocrine glands of the body already. But you might have noticed there’s
one last endocrine gland that we should mention that plays a vital role in our body
that’s called the pancreas.
The pancreas is unique because
parts of it act as an exocrine gland, secreting enzymes to support digestion,
whereas other endocrine cells secrete hormones into the blood. The hormones that are secreted by
the pancreas are involved in controlling the level of glucose in the blood. When we eat food, it travels
through our digestive system where some of it is broken down into glucose. This glucose then dissolves in the
bloodstream. Glucose can then be delivered via
the blood to all the body cells that need it. This allows the cells to release
energy through cellular respiration. To be able to take up glucose from
the blood, most cells of our body, like our muscle cells, need to receive a hormone
that’s produced by the pancreas. This hormone is called insulin.
The glucose that is not used by the
cells is stored in the liver in the form of glycogen. This provides an energy source that
can be used at a later date when no food is available, for example, during periods
of fasting. When no food is available to the
body, the level of glucose in the blood decreases. This triggers other cells in the
pancreas to release a different hormone called glucagon, which directs the liver to
break down glycogen into glucose. Glucose can be then released into
the blood to return blood glucose to a normal level. In this manner, the hormones
insulin and glucagon can keep glucose within a normal range. Now that we know more about the
main endocrine glands of the body, let’s see how much we’ve learned by applying our
knowledge to some practice questions.
Which of the following are two
hormones secreted by the pituitary gland? (A) Growth hormone and
thyroid-stimulating hormone, (B) calcitonin and insulin, (C) growth hormone and
insulin, or (D) thyroid-stimulating hormone and thyroxine.
Hormones are chemical messengers
that are produced in endocrine glands and secreted into the bloodstream. Once in the blood, they can travel
around the body to cause an effect on specific target cells. These effects include responses
that regulate bodily functions to adapt to changes in the internal and external
environment to maintain the normal functioning of the body. Let’s take a look at some specific
endocrine glands within the human body to work out which of the hormones are
secreted by the pituitary gland.
The pancreas is an endocrine gland
that secretes a hormone called insulin. Insulin is involved in regulating
blood glucose levels. As we know that this hormone is not
secreted by the pituitary gland but by the pancreas, we can eliminate options (B)
and (C). The thyroid gland is a
butterfly-shaped endocrine gland located at the front base of the neck. The thyroid gland secretes a
hormone called thyroxine, which is involved in energy metabolism. It also secretes a hormone called
calcitonin, which is involved in regulating the level of calcium in our blood. As we know that thyroid gland and
not the pituitary gland secretes thyroxine, we can also eliminate option (D).
The pituitary gland is a pea-sized
endocrine gland located just under the brain. It secretes a number of different
hormones, some of which can control other endocrine glands. For this reason, the pituitary
gland is sometimes called the master gland. One such hormone is
thyroid-stimulating hormone, sometimes called TSH, which stimulates the thyroid
gland to release the thyroid hormones. The pituitary gland also releases a
hormone called growth hormone that plays a role in the growth of tissues. Therefore, we’ve worked out that
growth hormone and thyroid-stimulating hormone are two hormones that the pituitary
gland can secrete.
Let’s try another practice question
together.
The figure shows changes in the
endometrium of the uterus during a 28-day menstrual cycle. Which hormone stimulates the
thickening of the uterine lining, endometrium, from day 19 to 28? (A) Testosterone, (B) progesterone,
(C) glucagon, (D) thyroid hormone, or (E) growth hormone.
The pituitary gland is an endocrine
gland that’s located just under the brain. It’s sometimes called the master
gland as it can secrete hormones that have effects on other endocrine glands. In biological females, one of these
endocrine glands that the pituitary gland hormones can target are the ovaries. The pituitary gland secretes
hormones called gonadotropins. In biological females,
gonadotropins regulate the production of the hormones estrogen and progesterone in
the ovaries. Estrogen is involved in the
development of secondary sex characteristics when a person reaches puberty.
In females, this might include the
development of breasts and starting the menstrual cycle. Estrogen also plays a part in
regulating the menstrual cycle, which is shown in the diagram as provided to us by
the question. During the menstrual cycle, an egg
cell is released from one of the ovaries in a process called ovulation. During this time, the uterine
lining, which is otherwise known as the endometrium, thickens to be prepared if an
egg cell is fertilized by a sperm cell. This is because a resulting embryo
if this fertilization occurs will implant into the endometrium. Progesterone is the hormone that’s
responsible for thickening this endometrium layer from day 19 to approximately day
28 of the menstrual cycle.
If pregnancy occurs, progesterone
levels remain high, so the endometrium layer remains thick to support the
development of the baby. However, if fertilization, and
therefore pregnancy, does not occur, then the endometrium is shed through a process
called menstruation or sometimes a period. This begins the menstrual cycle
again, and then the uterine lining will thicken once more as the levels of
progesterone start to increase again. Therefore, we’ve worked out that
the hormone that stimulates the thickening of the uterine lining or the endometrium
during the menstrual cycle is progesterone.
Let’s try one more question
together.
The figure shows some of the body’s
responses to fear and stress, which are coordinated by one main hormone X. What is hormone X? (A) Glucagon, (B) insulin, (C)
adrenaline, (D) testosterone, or (E) thyroxine.
Hormones are chemical messengers
that travel throughout the body via the bloodstream to cause an effect. They have diverse functions, and
each hormone has a specific target. Some hormones can be involved in
reproduction, growth, homoeostasis, and some in response to fear and stress caused
by dangerous situations. Hormones are secreted by endocrine
glands, an example of which are the adrenal glands. Humans typically have two adrenal
glands, one of which sits above each of our kidneys. Depending on the situation, the
adrenal glands can produce two main responses to cope with stress. One of these responses involves the
release of the hormone cortisol. Cortisol is used in more long-term
responses, modulating our metabolism and immune response.
The other response involves the
hormone adrenaline. It’s a short-term response produced
to react to acute stress or immediate danger. Adrenaline induces the
fight-or-flight response, which has many functions in the body. It can increase the blood flow to
muscles, increase the heart rate, and can even dilate the bronchioles, which are the
air passages leading to the lungs, allowing more oxygen to enter the
bloodstream. This is how our body prepares to
fight through or escape from a dangerous situation. Therefore, we’ve worked out that
hormone X is adrenaline.
Let’s summarize what we’ve learned
in this video. Hormones are chemical messengers
that travel in the blood to coordinate different responses. The pituitary gland produces many
hormones and can control the action of other endocrine glands. Some examples of hormones produced
by the pituitary gland are growth hormone, prolactin, oxytocin, and
thyroid-stimulating hormone. Thyroid-stimulating hormone
stimulates the thyroid gland to release thyroxine. To control the level of calcium in
the blood, the thyroid gland also releases the hormone calcitonin.
The pancreas secretes two main
hormones that are involved in glucose homoeostasis, insulin and glucagon. The adrenal glands produce many
hormones, one of which is involved in the fight-or-flight response to stressful
situations, adrenaline. The gonads include the testes in
biological males and the ovaries in biological females. While the testes mainly secrete
testosterone, the ovaries mainly secrete estrogen and progesterone.