Lesson Explainer: Action of Hormones Science

In this explainer, 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.

Hormones are involved in many different life processes. They can control how hungry you are, how sleepy you are, and how tall or short you are. They are critical in the functions of the reproductive, immune, and digestive systems. Without hormones, the food you eat would not be turned into fuel!

Key Term: Hormone

Hormones are chemical messengers that travel around an organism’s body, usually in the blood or another transport medium, to coordinate and regulate different responses.

Humans, and other multicellular organisms, can have different tissues and organs that perform certain functions. Within the bodies of multicellular organisms, constant and safe conditions must be maintained. 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 are outside in the cold, your body may shiver to generate heat to maintain its internal temperature. Homeostasis ensures that the body is functioning optimally. All organisms regulate their internal environments in order to survive.

Key Term: Homeostasis

Homeostasis is the maintenance of a constant, normal internal environment within an organism.

Example 1: Recalling the Definition for Homeostasis

Many endocrine responses keep the body’s internal environment stable.

What term describes how the body maintains constant conditions, such as blood glucose and water concentration?

  1. Balance
  2. Homeostasis
  3. Self-regulation
  4. Equilibrium

Answer

In order to survive, our body must be kept within specific parameters despite changes in the outside environment. This is called homeostasis.

For example, when we eat food, it is digested and sugars are extracted into our bloodstream. These sugars can be absorbed by cells in our body to be used for energy. This needs to happen because high levels of glucose in the blood can be dangerous.

In this situation, the body needs a communication system to regulate blood sugar levels to maintain homeostasis.

The endocrine system uses chemical messengers called hormones to relay messages. In this example, the hormone insulin can be released by the pancreas to tell cells to absorb glucose.

Therefore, the term that describes how the body maintains constant conditions is B: homeostasis.

In order to maintain homeostasis, there needs to be communication systems in place to send and receive different signals. There are two main communication systems: the nervous system and the endocrine, or hormonal, system.

The nervous system is able to coordinate responses using nerve impulses. For example, if your hand grabs for a plate that is too hot, your nervous system will communicate with the muscles in your hand to retract so you do not injure yourself. This happens very quickly.

Instead of nerve impulses, the endocrine system uses hormones to send messages. Hormones are chemical messengers that can travel through the blood to coordinate and regulate different responses.

Hormones are secreted in the blood by specialized glands called endocrine glands. In humans, some of the main endocrine glands include the pancreas, the ovaries and testes, the adrenal glands, and the pituitary gland. You can see their locations in Figure 1.

Key Term: Endocrine Gland

An endocrine gland is a group of specialized cells that secrete hormones into the blood.

Example 2: Identifying Endocrine Glands in the Human Body

The figure shows some of the main endocrine glands in the body.

  1. Which organ (A, B, C, D, or E) is the adrenal gland?
  2. What is endocrine gland X?

Answer

Part 1

Endocrine glands secrete hormones that can act as chemical messengers to regulate different processes in the body.

The main endocrine glands include the pancreas, the ovaries and testes, the adrenal gland, and the pituitary gland. You can see these glands and more in the image below.

Therefore, the adrenal gland is indicated by C in the diagram.

Part 2

Based on the above response in part 1, we can conclude that organ X corresponds to the thyroid.

Endocrine glands work like other glands. A gland is an organ that produces and secretes substances with different functions into the body. There are different types of glands in the human body that you can see in Figure 2 below.

Many glands have a tube or duct to deliver their secretions. For example, salivary glands are exocrine glands that secrete saliva through a duct, while sweat glands have a long tube that secretes sweat.

Unlike other glands, the endocrine glands do not use a tube or duct to deliver their secretions. This is why they are sometimes called ductless glands. Instead, their secretions are produced directly into the bloodstream. You can see this in the Figure 3 below.

Key Term: Ductless Glands

Ductless glands, like endocrine glands, secrete their products directly into the bloodstream without using a duct or tube.

Example 3: Recalling the Structure of an Endocrine Gland

The figure shows three different types of glands.

  1. Which image, A, B, or C, is an endocrine gland?
  2. What feature, shown in the image, is common to all endocrine glands?
    1. They have a space where the hormone is secreted.
    2. They have cells of different sizes.
    3. They do not have ducts.
    4. They have a long tube-like structure.

Answer

Part 1

Endocrine glands secrete hormones that can act as chemical messengers to regulate different processes in the body.

The main endocrine glands include the pancreas, the ovaries and testes, the adrenal gland, and the pituitary gland.

A gland is a specialized organ that secretes substances that can have different functions. Many glands have tubes or ducts that are used during secretion. For example, a salivary gland is an exocrine gland that secretes saliva through a duct, while a sweat gland uses a tube to secrete sweat. You can see this in the labeled image below.

Endocrine glands do not use tubes or ducts, and instead, their hormones are secreted directly into the bloodstream. For this reason, they are sometimes called ductless glands.

Therefore, the label corresponding to A is the endocrine gland.

Part 2

Based on the above response, we can conclude that all endocrine glands do not have ducts. Therefore, C is our correct answer.

Each endocrine gland produces one or more hormones. These hormones can then be secreted into the bloodstream to travel to specific organs where they can have an effect. These are called the target organs of the hormone.

Key Term: Target Organs

Target organs are the organs that are affected by hormones.

Since hormones are secreted into the bloodstream, they are able to act on their target organs anywhere in the body. However, this type of communication can be slow since the hormones need to be secreted and need to travel to their target organs.

Let’s look at some examples of the hormones produced by some different endocrine glands. You can look at Figure 1 to see their locations.

The pituitary gland is a pea-sized gland located at the base of the brain. It is sometimes called the master gland as it secretes hormones that can control the actions of other endocrine glands, like the ovaries for example. The target organs of the pituitary gland are not only other endocrine glands but also all kinds of tissues in the body. For example, the pituitary gland can also secrete growth hormone, which is involved in tissue growth and cell regeneration.

The thyroid is a butterfly-shaped gland located on the front base of the neck. It controls vital functions in the body, like how we consume our energy and our body temperature.

The adrenal glands are two pyramid-shaped glands, each located on top of the kidney. They both produce adrenaline, a hormone involved in the fight-or-flight response. This hormone can target muscle cells to increase blood flow in order to prepare for a potentially dangerous situation.

The pancreas looks like a long spongy leaf located under the stomach. It produces insulin, which is involved in regulating blood sugar levels. When you eat food, it is broken down into glucose and dissolved in the bloodstream. Insulin is a hormone that tells the cells of your body to absorb glucose to be used for energy. By absorbing glucose, the blood glucose levels drop and return to normal.

All endocrine glands of the body are very similar in size and shape between males and females, except for the sexual glands! The testes and ovaries can produce hormones involved in the development of the male or female reproductive system. The testes in the male produce testosterone, and the ovaries in the female produce estrogen and progesterone that play an important role in puberty and in the female’s reproductive life.

We will look at these glands and hormones in greater detail in another lesson.

Example 4: Identifying Endocrine Glands and Their Secretions

The figure shows some of the main endocrine glands in the body.

  1. Which endocrine organ (A, B, C, D, or E) secretes growth hormone?
  2. Which endocrine organ (A, B, C, D, or E) controls blood sugar levels?

Answer

Part 1

Endocrine glands secrete hormones that can act as chemical messengers to regulate different processes in the body.

The main endocrine glands include the pancreas, the ovaries and testes, the adrenal gland, and the pituitary gland. You can see these glands and more in the image below.

Different endocrine glands can secrete different hormones. Growth hormone is involved in tissue growth and regeneration and is secreted by the pituitary gland.

Therefore, the endocrine organ labeled A is the endocrine gland that secretes growth hormone (the pituitary gland).

Part 2

Different endocrine glands can secrete different hormones. Insulin is secreted by the pancreas and controls blood sugar levels. Insulin tells cells to absorb glucose to be used for energy production. By absorbing the glucose, the blood glucose levels drop back to normal levels.

Therefore, the endocrine organ labeled D is the endocrine gland that secretes insulin to control blood sugar levels (the pancreas).

Let’s recap some of the key points we have covered in this explainer.

Key Points

  • Hormones play a role in homeostasis, the body’s way of maintaining its internal environment.
  • Hormones are produced and secreted by endocrine glands, also called ductless glands.
  • Endocrine glands secrete hormones into the blood where they can travel and affect their target organs.
  • The pituitary gland is sometimes called the master gland because it can control the actions of other endocrine glands.

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