Video Transcript
In this video, we will learn about
the different components of the human endocrine system. We will investigate some examples
of endocrine glands and the different hormones that they secrete to regulate and
maintain our body’s internal environment.
Hormones are involved in many
different life processes. They can control how hungry you
are, how sleepy you are, and even play a role in determining how tall or short you
are. Hormones are critical in the
function of the reproductive system, the immune system, and the digestive
system. In fact, without hormones, the food
we eat could not be used as an energy source.
Hormones are chemical messengers
that travel around the body usually in the bloodstream or sometimes in another
transport medium to coordinate and regulate responses. Hormones are produced and secreted
by endocrine glands. These are specialized groups of
cells that secrete hormones directly into the blood. The blood stream then transports
these hormones throughout the body. Hormones are usually dissolved in
the liquid portion of blood, which is called plasma. The blood transports these hormones
throughout the body and to specific cells called target cells, which can produce a
specific response.
All glands within the body release
a substance with a specific function. Let’s compare these different
glands by first summarizing what we know about endocrine glands. They produce and secrete
hormones. And these secretions enter the
blood directly, which transports them to their target cells.
Another type of gland in the human
body are called exocrine glands, so let’s explore these next. Exocrine glands work slightly
differently, as they do not release hormones into the blood. Instead, they produce and secrete
substances, like enzymes, for example, via tube-like structures called ducts onto
body surfaces that can either be internal or external. Let’s see what this means with an
example.
Salivary glands are located close
to our mouths. They secrete a substance called
saliva, which contains enzymes. These enzymes are released onto the
inner surface of our mouth to help break down carbohydrates in our food. And saliva is released via salivary
ducts. Another example is the sweat glands
that are found just below the surface of most of our skin. These are also exocrine glands as
they secrete a substance called sweat onto the outer surface of our skin to help
cool us down when we’re too hot. And sweat is also secreted via
ducts. As endocrine glands do not secrete
substances via ducts, they are sometimes called ductless glands.
Let’s take a quick look at a major
role that hormones can carry out in the human body. Humans and other multicellular
organisms can have different tissues and organs that perform certain functions. Within the bodies of multicellular
organisms, constant, normal, and safe internal conditions must be maintained within
a fairly narrow range, for instance, making sure our core body temperature does not
get too hot or too cold. Hormones play an important role in
maintaining these conditions, a process known as homeostasis.
Homeostasis is the body’s way of
keeping its internal environment stable despite changes outside of the body. For example, if you’re outside in
the cold, your body may begin to shiver to generate heat and maintain its internal
temperature. Homeostasis ensures that the body
is functioning optimally. And all organisms, not just humans,
regulate their internal environments in order to survive. In order to maintain homeostasis,
there need to be communication systems in place in the body to send and receive
different signals. The two main communication systems
in the human body are the nervous system that sends electrical signals around the
body and the endocrine or hormonal system, which is the focus of this video in
humans.
Some of the main endocrine glands
include the pituitary gland, the thyroid gland, the adrenal glands, the pancreas,
the testes in biological males, and the ovaries in biological females. Each endocrine gland produces one
or more hormones. These hormones can then be secreted
into the blood stream to travel to different specific target organs to cause a
specific effect. As these hormones first need to be
produced and then secreted and then transported sometimes fairly long distances,
this process can be quite slow. Let’s take a look at some of the
hormones that are produced and secreted by some of these different endocrine
glands.
The pituitary gland is a pea-sized
gland located at the base of the brain. It is sometimes called the master
gland, as it can secrete hormones that control the actions of other endocrine
glands, like the ovaries for example. The target cells of pituitary gland
hormones and not just found in other endocrine glands, however, but many tissues all
over the body. For example, the pituitary gland
can secrete growth hormone, which is involved in tissue growth and cell
regeneration.
The thyroid gland is a
butterfly-shaped gland located at the front base of our neck. Thyroid hormones control vital
functions in the body, like our body temperature. They also play a role in how we
metabolize food and consume energy in our cells. Thyroid hormones may even have an
effect on our heart rate.
The adrenal glands are too vaguely
pyramid-shaped glands, one of which is located on top of each of our kidneys. They produce and secrete many
different hormones, but one you may well have heard of is adrenaline, which is the
hormone involved in the fight-or-flight response. This hormone can target muscle
cells to increase their blood supply and also their use of energy in order to
prepare our body to fight through or escape from a potentially dangerous or
stressful situation.
The pancreas is an elongated organ
that forms part of our digestive system. It’s located just under the
stomach. One of the hormones that produces
and secretes is called insulin, which is involved in regulating blood sugar
levels. Insulin is a hormone that tells the
cells of our body to absorb the glucose that we obtained from sugars in our food to
be used for energy. By absorbing glucose, the blood
glucose levels can drop and return to normal when they become too high. The pancreas is a super interesting
gland, as it can also technically function as an exocrine gland by secreted enzymes
into the small intestine to help with digestion. For this reason, the pancreas is
sometimes called a mixed gland, as it carries out both endocrine and exocrine
functions.
All endocrine glands of the body
are very similar in size and shape between biological males and biological females,
except for the sexual glands, which are sometimes known as the reproductive glands
or the gonads. The testes and the ovaries both
produce and secrete hormones involved in the development of the male or female
reproductive systems. The testes in the male reproductive
system produce testosterone, and the ovaries in the female reproductive system
produce estrogen and progesterone. All of these hormones play an
important role in the development of the sex organs and in puberty in both
biological sexes. And the typically female sex
hormones have additional functions later on in the female’s reproductive life.
Let’s see how much we’ve learned
about the action of hormones by applying our knowledge to a few practice
questions.
The figure shows some of the main
endocrine glands in the body. Which organ (A), (B), (C), (D), or
(E) is the adrenal gland? What is endocrine gland X?
To answer these questions, we first
need to know what an endocrine gland is. Endocrine glands are groups of
specialized cells that secrete hormones into the bloodstream. Hormones are chemical messengers
that can cause a response elsewhere in the body from where they’re produced in order
to regulate different processes in the human body. Let’s take a look at the different
endocrine glands that are shown in this diagram so that we can identify which one is
the adrenal gland.
Organ (A) is a testis, and organ
(B) is an ovary. These two organs are collectively
known as the gonads. While each of the two testes are
responsible for producing and secreting the male sex hormones mainly, the two
ovaries are responsible for producing and secreting the female sex hormones
primarily. Organ (C) is one of the two adrenal
glands. These glands are responsible for
producing many hormones, one of which is adrenaline that controls the
fight-or-flight response in stressful situations. Organ (D) is the pancreas. The pancreas also releases several
hormones, one of which is insulin that can control our blood sugar level when it
becomes too high. Organ (E) is the pituitary
gland. This is sometimes referred to as
the master gland, as it releases several hormones that can control other glands. Therefore, we’ve deduced that organ
(C) is the adrenal gland.
Let’s have a go at the next part of
the question. The final gland that we haven’t yet
labeled on the diagram, organ X, is the thyroid gland. This gland is responsible for
releasing thyroid hormones, which have a number of different effects including on
our metabolism and even our heart rate. So we can conclude that organ X
corresponds to the thyroid gland.
Let’s have a go at another practice
question together.
The figure shows some of the main
endocrine glands in the body. Which endocrine organ (A), (B),
(C), (D), or (E) secretes growth hormone? Which endocrine organ (A), (B),
(C), (D), or (E) controls blood sugar levels?
To answer this question, we need to
be able to identify some of the endocrine glands that are shown in this image, the
hormones they release, and the functions of these hormones. So let’s get started. Organ (A) is the pituitary gland,
located at the base of the brain. The pituitary gland is sometimes
called the master gland as it releases hormones that can have an effect on many of
the other endocrine glands. One of the hormones it releases is
called growth hormone. The main function of growth hormone
is to control tissue growth and cell regeneration. Therefore it’s a really important
hormone in human development. So we’ve worked out the answer to
the first part of the question. Which endocrine organs secrete
growth hormone? It’s organ (A), the pituitary
gland.
Let’s have a go at the second part
of the question now. The organ labeled as (D) is called
the pancreas. The pancreas also releases several
hormones, one of which is called insulin. Insulin is partly responsible for
maintaining blood sugar level within a healthy range. In fact, if blood sugar levels
become too high, insulin functions to lower blood sugar levels back to a normal
level. So we’ve worked out the second part
of the question that the endocrine organ that controls blood sugar levels is (D),
the pancreas.
Let’s try one final practice
question together.
The figure shows three different
types of glands. Which image (A), (B), or (C) is an
endocrine gland? What feature shown in the image is
common to all endocrine glands? (A) They do not have ducts. (B) They have cells of different
sizes. (C) They have a long, tube-like
structure. Or (D) They have a space where the
hormone is secreted.
An endocrine gland is a group of
specialized cells that secrete hormones directly into the bloodstream. These hormones can then control and
regulate different processes in the human body. In order to identify which image is
showing an endocrine gland, let’s look at the key features in each of the
images.
In image (A), we can see some blood
vessels. In both Image (B) and image (C), we
can see a long, tube-like structure called a duct. We can also see in both of these
images that some kind of secretion is being made onto a body surface. However, in images (B) and (C), we
cannot see any blood vessels. As we know that endocrine glands
secrete hormones directly into the bloodstream, we can work out that the image
showing an endocrine gland, which is closely associated with blood vessels, is Image
(A).
Let’s try the second part of the
question. We’ve already identified that image
(A) is showing us an endocrine gland. But what about images (B) and
(C)? These are both showing examples of
exocrine glands, which are groups of specialized cells that secrete substances via
ducts onto body surfaces. For example, image (B) is a
salivary gland secreting saliva via the salivary duct into the mouth, which is an
internal body surface. Image (C) displays a sweat gland
secreting sweat via sweat ducts onto the external body surface that is the skin.
A common feature of all endocrine
glands is that, unlike exocrine glands, they do not possess ducts. So they’re sometimes called
ductless glands. They don’t necessarily have cells
of different sizes, and they do not have long, tube-like structures, as this is
describing a duct. As you can also see in image (A),
they do not have a space into which the hormone is secreted. Instead, they secrete the hormones
directly into the blood. So we’ve worked out that the common
feature to all endocrine glands that’s shown in this image is that they do not have
ducts.
Now it’s time to wrap up the video
by reviewing the key points that we’ve looked at about the action of hormones. Hormones are involved in
homeostasis, which is the body’s way to help maintain a normal, constant, internal
environment. Endocrine glands secrete hormones
into the blood, where they can travel to and affect their target organs. Some examples of endocrine glands
include the pituitary gland, which is sometimes called the master gland; the thyroid
gland; the adrenal glands; the pancreas, which also has exocrine functions; the
female ovaries; and the male testes.
