Lesson Explainer: Hormones and Disease Science

In this explainer, we will learn how to describe examples of diseases caused by the malfunction of endocrine glands and outline how these diseases can be treated.

If the person in the picture below looks familiar to you, then this is because this is the Argentinian footballer Lionel Messi. While most people may know him from his athletic career, what you may not know is that Messi is one of the only athletes that was allowed to take human growth hormone and still play competitively.

Lionel Messi of Barcelona during the Spanish Cup-500
Figure 1

Using human growth hormone is banned for adult athletes because it can help speed up the growth of muscles. However, Messi’s use of growth hormone was to help treat his growth hormone disorder. Since this type of disorder occurs as a result of a malfunction in a gland in the endocrine system, Messi had a therapeutic exemption.

You may recall that the endocrine system is a group of glands throughout the human body that secrete hormones into the bloodstream. Since hormones are secreted into the bloodstream, they are very powerful because even a small amount can cause large changes in cells, organs, or even the whole body. Such a powerful effect of hormones also means that any imbalance in your hormones, either too much or too little, can be serious, especially if this imbalance is due to a malfunction in the pancreas or in the pituitary or thyroid gland.

In Messi’s case, the source of his growth hormone deficiency was a malfunction in his pituitary gland.

Key Term: Pituitary Gland

The pituitary gland, which is located in the brain, is a gland that secretes hormones that regulate other glands and tissues in the body.

Figure 2: A diagram showing the pituitary gland located at the base of the brain. This gland is called the master gland because of all the hormones it produces, which act on a variety of tissues in the body.

Growth hormone is one of the many hormones produced by the pituitary gland, as shown in Figure 2. As its name suggests, growth hormone (GH) is essential for normal growth and development. So, any malfunction in the release of GH can cause significant changes in growth and development during childhood.

Normally, GH is released into the bloodstream throughout the day, with peaks that occur during sleep at night. These nighttime peaks are why growing pains are felt the strongest while you are sleeping. Also, since the production of GH is highest during sleep, it is very important to sleep well, especially during childhood.

Key Term: Growth Hormone

Growth hormone is a hormone secreted by the pituitary gland that is involved in tissue growth.

When the pituitary gland malfunctions, this can cause various disorders, such as growth hormone deficiency (GHD), also called dwarfism. Without a sufficient amount of GH in the body, children with GHD stay abnormally short. For example, at the age of 11, when Lionel Messi was diagnosed with GHD, he was only 1.27 metres (49.9 inches) tall.

Definition: Dwarfism

Dwarfism is a condition that is caused by extremely low levels of growth hormone in developing children and results in short stature.

Without GH treatment, Messi was expected to grow to only 1.4 metres (55 inches) tall. However, with the help of treatment, he grew to be 1.68 metres (66 inches) tall. Children with GHD are treated with injections of growth hormone.

For Messi’s treatment, the growth hormone used was most likely made by genetically modified bacteria.

In the past, growth hormone was extracted from the pituitary glands of newly dead corpses. This method, however, allowed only a small amount of GH to be extracted, so it is not a very useful or sustainable source of GH for use in treatment.

However, in 1979, through advances in genetic engineering technology, researchers found a way to produce growth hormone using bacteria. Using this method, the human gene that controls the production of GH could be inserted into the DNA of a bacterial cell. With enough bacterial cells that have been modified to have the gene for GH, a large-enough quantity of microbe-free GH could be produced to treat disorders like GHD (dwarfism).

Key Term: Genetically Modified (GM) Bacteria

Genetically modified (GM) bacteria are created to include human genes to produce useful substances, such as hormones.

Pituitary gland malfunctions can also lead to an increase in GH. When too much GH is produced during childhood, this causes the long bones to grow well past puberty, resulting in a condition called gigantism. Children with gigantism can grow up to 2.13 metres (84 inches) or more in height.

The most common cause of gigantism is a noncancerous tumor on the pituitary gland. So, treatment of gigantism usually involves the removal or destruction (with lasers) of the pituitary tumor, which stops the overproduction of GH.

Definition: Gigantism

Gigantism is a condition caused by the overproduction of growth hormone in children and results in excessive height.

Example 1: Understanding the Effects of a Pituitary Tumor

What endocrine condition may develop as the result of a tumor in the pituitary gland?

  1. Gigantism
  2. Goiter
  3. Diabetes

Answer

You may recall that the endocrine system is a group of glands throughout the human body that secrete hormones into the bloodstream. Since hormones are secreted into the bloodstream, they are very powerful because even a small amount can cause large changes in cells, organs, or even the whole body. Such a powerful effect of hormones also means that any imbalance in your hormones, either too much or too little, can be serious, especially if this imbalance is due to a malfunction in the pancreas or in the pituitary or thyroid gland.

Growth hormone is produced by the pituitary gland. As its name suggests, growth hormone (GH) is essential for normal growth and development.

When the pituitary gland malfunctions, this can cause various disorders, such as growth hormone deficiency (GHD), also called dwarfism. Without a sufficient amount of GH in the body, children with GHD stay abnormally short.

Pituitary gland malfunctions can also lead to an increase in GH. When too much GH is produced during childhood, this causes the long bones to grow well past puberty, resulting in gigantism. In contrast to dwarfism, gigantism in children results in excessive height, with children sometimes reaching up to 2.13 metres (84 inches) or more in height.

The most common cause of gigantism is a noncancerous tumor on the pituitary gland. So, treatment of gigantism usually involves the removal or destruction (with lasers) of the pituitary tumor, which stops the overproduction of GH.

Therefore, the endocrine condition that may develop as a result of a tumor in the pituitary gland is gigantism.

Messi’s growth disorder is only one example of gland malfunction in the endocrine system. Let’s take a closer look at some other examples.

The pancreas is a gland within the endocrine system. This gland makes insulin and glucagon, which are the hormones that control the level of glucose in the blood. Glucose is considered an important energy resource in the body, so much that it is usually stored for later use. A summary of how insulin and glucagon balance blood glucose levels is shown below in Figure 3.

When the blood glucose level is too high, like after eating too much cake or candy, the pancreas detects this and produces insulin to be released into the bloodstream. The insulin travels to the liver, signaling the liver to turn excess glucose into glycogen. As glycogen is formed, the blood glucose level is lowered.

If the blood glucose level becomes too low, like after an intense exercise or a long school exam, glucagon is released by the pancreas and targets the liver and muscles. These hormone signals cause the liver and muscles to convert glycogen into glucose.

Figure 3: A diagram showing how insulin and glucagon are used to balance blood glucose levels.

Definition: Pancreas

The pancreas is an organ that secretes the hormones insulin and glucagon into the bloodstream.

Definition: Insulin

Insulin is a hormone that helps control the concentration of glucose in the blood.

When the pancreas malfunctions, this causes a halt in the production of insulin, resulting in diabetes.

Diabetes is a disease that occurs when the pancreas malfunctions and stops producing insulin. Without a sufficient amount of insulin secreted, the blood glucose level stays very high, which increases the patient’s thirst and urine output and makes them feel very tired more frequently. One of the more challenging aspects of diabetes is that since these symptoms develop over time, most people do not perceive them as problematic.

Definition: Diabetes

Diabetes is a disease in which a malfunction in the pancreas reduces or halts the production of insulin.

Several researchers have pointed out that diabetes occurs in two major ways.

Type 1 diabetes has no known cause but is believed to be a reaction in which the immune system mistakenly attacks a healthy tissue in the body. In this type of diabetes, the pancreas does not make insulin. Children or young adults are usually diagnosed with type 1 diabetes, and their symptoms have to be treated every day by taking insulin.

Type 2 diabetes usually develops later in life. In this type of diabetes, the cells become resistant to the action of insulin. Without insulin, blood glucose cannot move into the cells where it is needed for energy production. This leads to a buildup of blood glucose in the bloodstream.

Figure 4 compares the differences in the two types of diabetes with a healthy person.

Figure 4: A diagram showing the differences between the types of diabetes.

If the pancreas does not produce insulin, something as simple as ingesting a sugary drink, like a soda, can be dangerous. The graph in Figure 5 shows the difference in blood glucose concentrations when a healthy person ingests a sugary drink in comparison to a diabetic person.

In the graph, the 𝑦-axis represents the level of blood glucose and the 𝑥-axis represents the time in hours.

Figure 5: A graph showing the difference in the blood glucose concentration after consuming a sugary drink between a healthy person and a person with diabetes.

In a healthy person, after drinking a sugary drink, a rapid rise occurs in the blood glucose levels, until reaching the peak about one hour later. Then, after an hour, the blood glucose concentration begins to rapidly fall, due to the production of insulin by the pancreas. The action of insulin is so strong that, two hours after consuming the sugary drink, the concentration of blood glucose, which has fallen below normal blood glucose levels, stays very low.

In a person with diabetes, the pancreas no longer produces insulin or their cells may be resistant to insulin.

So, after ingesting a sugary drink, a rapid rise occurs in the blood glucose levels. However, without the action of insulin, this blood glucose cannot be converted into glycogen and stored in the liver. So, the blood glucose levels remain very high for several hours.

It is this persistently high level of blood glucose in a person with diabetes that causes serious health issues, such as heart disease or stroke.

As shown in the graph, blood glucose levels are very hard to control without insulin. This is why some treatments for diabetic people include injections of insulin. However, this course of treatment only works when someone has type 1 diabetes. In type 2 diabetes, since the cells are resistant to absorbing insulin, injecting it in any quantity does not work.

Example 2: Charting Blood Glucose Changes in Diabetes

The chart shows the changes in blood glucose levels after two comparable patients consume the same amount of a sugary drink. The blood glucose level of the diabetic patient is represented in green, and the blood glucose level of the healthy patient is represented in pink.

After the diabetic patient absorbs the sugary drink, what could explain why their level of glucose remains higher for a longer time than that of the healthy patient?

  1. Due to the lack of insulin, the body cells of the diabetic patient do not absorb blood glucose effectively.
  2. The pancreas of the diabetic patient releases too much glucose.
  3. The liver cells of the diabetic patient do not release enough insulin.
  4. The diabetic patient has too much insulin.

Answer

Diabetes is a disease that occurs when the pancreas malfunctions and stops producing insulin. Without a sufficient amount of insulin secreted, the blood glucose level stays very high, which increases the patient’s thirst and urine output and makes them feel very tired more frequently. One of the more challenging aspects of diabetes is that since these symptoms develop over time, most people do not perceive them as problematic.

In the graph, the 𝑦-axis represents the level of blood glucose and the 𝑥-axis represents the time in hours. There are three differences, visible on the graph, between the response of a healthy person and that of a diabetic person.

In a healthy person, after drinking a sugary drink, a rapid rise occurs in the blood glucose levels, until reaching the peak about one hour later. Then, after an hour, the blood glucose level begins to rapidly fall, due to the production of insulin by the pancreas. The action of insulin is so strong that, two hours after consuming the sugary drink, the concentration of blood glucose, which has fallen below normal blood glucose levels, stays very low.

In a person with diabetes, the pancreas no longer produces insulin or their cells may be resistant to insulin. So, after drinking a sugary drink, a rapid rise occurs in the blood glucose levels, which lasts for an hour. After this initial rise, the blood glucose concentrations do not decrease and rather stay very high. This is because, without the action of insulin, blood glucose cannot be converted into glycogen and stored in the liver. So, the blood glucose levels remain very high for several hours.

It is this persistently high level of blood glucose in a person with diabetes that causes serious health issues, such as heart disease or stroke.

Therefore, the level of glucose in the diabetic patient stays high one hour after ingesting the sugary drink because due to the lack of insulin, the body cells of the diabetic patient do not absorb blood glucose effectively.

The last example of endocrine system dysfunction comes from the thyroid gland.

As you may recall, the thyroid is one of the largest glands of the endocrine system. The thyroid gland produces hormones that control how quickly your body uses energy, speed of protein production, and sensitivity to other hormones. To exert this control, the thyroid gland secretes the hormone thyroxine.

Since thyroxine controls the release of energy from food, both over- and undersecretion of thyroxine can cause the gland to enlarge, form goiters, and make you sick.

Key Term: Thyroid Gland

The thyroid gland produces hormones that control how quickly your body uses energy, speed of protein production, and sensitivity to other hormones.

Key Term: Thyroxine

Thyroxine is the main hormone produced by the thyroid gland.

The thyroid gland, found in the front of your neck, is a butterfly-shaped gland controlled by the pituitary gland found in the brain. In addition to being controlled by the pituitary gland, the thyroid gland needs the mineral iodine to function properly. However, the body does not produce iodine, so the only source of iodine is from the food we eat.

If your diet does not include iodine, then your thyroid gland will be less able to produce thyroxine.

When the amount of thyroxine being secreted is low, the pituitary gland tries to stimulate more by releasing more thyroid-stimulating hormone. However, since the thyroid gland is not working properly, this increase in thyroid-stimulating hormone causes it to build up in the thyroid gland, causing it to become enlarged and form a simple goiter. Figure 6 shows the difference in size between a healthy thyroid gland and an enlarged one.

Figure 6: A diagram showing the change in size in the thyroid gland, which is located at the front of the neck. Overproduction of thyroid-stimulating hormone causes it to build up, eventually causing a simple goiter.

Key Term: Iodine

Iodine is a mineral found in food that is required for the proper functioning of the thyroid gland.

Definition: Simple Goiter

A simple goiter is the enlargement of the thyroid gland that is usually due to iodine deficiency.

Example 3: Identifying the Reason for an Enlarged Thyroid Gland

The figure shows how the thyroid gland can become enlarged, forming a goiter.

What nutrient deficiency may lead to the formation of an enlarged thyroid, as shown in the figure?

  1. Iron
  2. Protein
  3. Calcium
  4. Vitamin D
  5. Iodine

Answer

As you may recall, the thyroid is one of the largest glands of the endocrine system. This gland, which is found in your neck, is controlled by the pituitary gland found in the brain. The thyroid gland produces hormones that control how quickly your body uses energy, speed of protein production, and sensitivity to other hormones.

In addition to being controlled by the pituitary gland, the thyroid gland needs the mineral iodine to function properly. However, the body does not produce iodine, so the only source of iodine is from the food we eat. If your diet does not include iodine, your thyroid gland will be less able to produce thyroxine.

When the amount of thyroxine being secreted is low, the pituitary gland tries to stimulate more by releasing more thyroid-stimulating hormone. However, since the thyroid gland is not working properly, this increase in thyroid-stimulating hormone causes it to build up in the thyroid gland, causing it to become enlarged and form a goiter.

Therefore, the nutrient whose deficiency may lead to the formation of an enlarged thyroid, forming a goiter, is iodine.

A malfunction of the thyroid gland can also cause excessive secretion of thyroxine, which causes an exophthalmic goiter. This type of goiter also causes weight loss, an increase in heart rate, and irritability. There is one additional symptom that can help doctors tell the difference between simple and exophthalmic goiters.

The word exophthalmic refers to “bulging eyes,” which are observed with this type of goiter. This symptom can help doctors identify the correct treatment plan.

If a patient with a goiter also has bulging eyes, as shown in Figure 7, this can indicate that the goiter is part of a reaction where the immune system mistakenly attacks a healthy tissue in the body. This type of goiter would require a change in the treatment plan. For a goiter that includes bulging eyes as a symptom, doctors can surgically remove part of the gland to reduce thyroxine production rather than treating it with diet changes.

Figure 7: A diagram showing the symptoms associated with an exophthalmic goiter. This type of goiter is usually associated with a disorder.

Key Term: Exophthalmic Goiter

An exophthalmic goiter is a type of goiter caused by excessive thyroxine production and usually also causes the eyes to bulge.

Example 4: Describing the Symptoms of an Exophthalmic Goiter

The figure shows the appearance of a person with an enlarged thyroid gland.

  1. What is the name for this disease condition?
    1. Exophthalmic goiter
    2. Dwarfism
    3. Simple goiter
    4. Gigantism
    5. Diabetes
  2. What is the cause of the bulging of the eyes?
    1. Too little thyroxine
    2. Too much thyroxine
    3. Too little growth hormone
    4. Too much growth hormone

Answer

As you may recall, the thyroid is one of the largest glands of the endocrine system. This gland, which is found in your neck, is controlled by the pituitary gland found in the brain. The thyroid gland produces hormones that control how quickly your body uses energy, speed of protein production, and sensitivity to other hormones.

Part 1

A malfunction of the thyroid gland can cause excessive secretion of thyroxine. This causes the thyroid gland to become enlarged and causes a goiter (of the exophthalmic type). To differentiate between this type of goiter and a regular goiter, doctors usually examine the eyes.

Therefore, the name of the disease condition shown in the picture is exophthalmic goiter.

Part 2

If a patient with a goiter also has bulging eyes, this may indicate that the goiter is part of a disorder that causes excessive secretion of thyroxine and causes an exophthalmic goiter.

This type of goiter requires a change in the treatment plan. Doctors use radioactive iodine instead of changes in the diet to treat goiters that include bulging eyes as a symptom.

Therefore, the cause of eyes bulging is too much thyroxine.

Let’s review what we have learned in this explainer.

Key Points

  • Some diseases are caused by a malfunction in endocrine glands.
  • When the pituitary gland malfunctions, the levels of growth hormone in the body can change.
  • In children, a very low level of growth hormone causes dwarfism, whereas an excess amount causes gigantism.
  • Diabetes is a disease that involves a malfunction in the pancreas, halting the production of insulin.
  • Type 1 diabetes usually affects children or young adults and is caused when the pancreas cannot produce insulin.
  • Type 2 diabetes usually affects people later on in life and is caused by cells becoming resistant to insulin.
  • Both over- and undersecretion of thyroxine by the thyroid gland can cause goiters to form.
  • Simple goiter is caused by a lack of iodine in the diet and a decrease in thyroxine levels.
  • Exophthalmic goiter is caused by excess thyroxine and is accompanied by bulging eyes.

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