Lesson Video: Action of Hormones Science

In this video, we will learn how to outline the components of the endocrine system and how it functions using specific examples of endocrine glands and the hormones that they secrete.


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.

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