Lesson Explainer: Hormones and the Body Science

In this explainer, we will learn how to describe the effects of different hormones produced by the pituitary gland and outline the specific functions of hormones produced by the thyroid gland, gonads, pancreas, and adrenal glands.

Do you have a pet? Some studies have found that by bonding with your pet, for example by cuddling or petting, both the human and the pet have a release of oxytocin. Oxytocin is sometimes called the love hormone because it brings feelings of happiness and trust. This hormone makes us feel good and might explain why we bond with pets!

Hormones are chemical messengers that can travel through the blood to coordinate and regulate different responses. They 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: Hormones

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.

Key Term: Endocrine Gland

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

The pituitary gland is located below the brain and is about the size of a pea. Even though it is small, it is sometimes called the master gland because it secretes hormones that regulate the functions of other endocrine glands.

The pituitary gland can secrete many hormones. Some pituitary hormones have a direct effect on target organs. Let’s look at the examples of growth hormone (GH), antidiuretic hormone (ADH), prolactin, thyroid-stimulating hormone (TSH), and oxytocin. Figure 2 shows these hormones being released from the pituitary gland and indicates the target organs they act upon.

Growth hormone is secreted by the pituitary gland and controls the growth of muscles, bones, and organs inside of your body. This is the hormone that helps determine how tall you are. Without enough growth hormone, dwarfism may occur. This is a medical condition where adults are short in height and do not grow much taller than about 122 cm.

Key Term: Growth Hormone

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

The pituitary gland also secretes antidiuretic hormone (ADH). This hormone tells your kidneys how much water to conserve. The concentration of water in your blood needs to be within a certain range and ADH can help maintain these levels.

Prolactin is a hormone that is involved in producing milk in the mammary glands of the breasts during pregnancy and after birth. In nonpregnant women, and in men, prolactin levels are low. Another hormone produced by the pituitary gland is thyroid-stimulating hormone (TSH). This hormone acts on the thyroid to produce hormones that are involved in energy metabolism like thyroxine, which will be discussed below.

Key Term: Prolactin

Prolactin is a hormone that is secreted by the pituitary gland and that is involved in lactation.

Oxytocin is a pituitary hormone that has many effects. It is involved in childbirth and is important in the widening of the cervix so the baby can pass through. As mentioned, oxytocin is also important in social bonding and emotional responses such as trust, empathy, and positive communication.

Key Term: Oxytocin

Oxytocin is a hormone that is secreted by the pituitary gland and that has multiple functions during childbirth and in social behavior and emotions.

Example 1: Recalling the Hormones of the Pituitary Gland

Which of the following are two hormones secreted by the pituitary gland?

  1. Growth hormone and thyroid-stimulating hormone
  2. Calcitonin and insulin
  3. Growth hormone and insulin
  4. Thyroid-stimulating hormone and thyroxine

Answer

Hormones are chemical messengers that travel through the blood to regulate different responses. They are secreted by endocrine glands, such as the pancreas, thyroid, and pituitary gland.

The pancreas can secrete insulin, which is involved in regulating blood glucose levels.

The thyroid can secrete calcitonin, which is involved in calcium homeostasis, as well as thyroxine, which is involved in energy metabolism.

The pituitary gland can secrete growth hormone that plays a role in the growth of tissues, as well as thyroid-stimulating hormone that can act on the thyroid to produce its hormones.

Therefore, growth hormone and thyroid-stimulating hormone are two hormones secreted by the pituitary gland.

The pituitary gland can also secrete hormones that control the activity of other endocrine glands such as the ovaries, testes, thyroid, and adrenal gland. Let’s look at how the pituitary gland can influence the activities of the ovaries and testes to produce sex hormones, as seen in Figure 3 below.

Puberty typically begins at ages 10 to 11 for females or at ages 11 to 12 in males and lasts for about 4 years. During this time, secondary sex characteristics like increased muscle mass in males and breast development in females develop. The pituitary gland acts on the testes to produce testosterone and the ovaries to produce estrogen, both of which are responsible for these characteristics.

Menstruation, also known as a period, typically begins during puberty in the female. During the menstrual cycle, an egg is released from the ovaries and the lining of the uterus, or the endometrium, builds up. If a pregnancy does not occur, then the endometrium sheds over 3 to 5 days during a menstrual period. The menstrual cycle is typically 28 days (although this can vary) and is due to the rise and fall of different hormones.

One of the hormones involved in the menstrual cycle is progesterone. Progesterone is secreted from the ovaries after it is stimulated by the pituitary gland. This hormone functions to thicken the endometrium to prepare it for pregnancy.

Key Term: Sex hormones (Estrogen, Testosterone, and Progesterone)

Sex hormones, such as estrogen, testosterone, and progesterone, are produced during puberty and are involved in the reproductive system.

Example 2: Recalling the Function of Specific Hormones during the Menstrual Cycle

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?

Answer

Hormones are chemical messengers that travel through the blood to regulate different responses. They are secreted by endocrine glands, such as the pancreas, pituitary gland, and the gonads, that is, the testes and ovaries.

The pituitary gland is able to regulate many different endocrine glands, and for this reason it is sometimes called the master gland. One of its targets are the ovaries.

The pituitary gland can regulate the production of the hormones estrogen and progesterone in the ovaries. Estrogen is involved in the development of secondary sex characteristics during puberty, like the development of breasts, and also plays a part during the menstrual cycle.

During the menstrual cycle, an egg is released from the ovaries in a process called ovulation, while the uterine lining, or endometrium, thickens. If the egg is fertilized by sperm, then the resulting embryo can implant into the endometrium to create a pregnancy. If a pregnancy does not occur, then the endometrium sheds during a menstrual period.

Menstruation typically occurs in a 28-day cycle and is regulated by different hormones, including estrogen and progesterone. Progesterone is the hormone that thickens the endometrium.

Therefore, the hormone that stimulates the thickening of the uterine lining (endometrium) during the menstrual cycle is progesterone.

Let’s look at some of the other endocrine glands and the hormones they produce.

The pancreas is unique because it can act as an exocrine gland and an endocrine gland. The cells of the pancreas can either secrete digestive enzymes in ducts (exocrine) or secrete hormones directly into the blood (endocrine). You can see this in Figure 4 below.

The hormones of the pancreas are involved in energy metabolism and glucose homeostasis. Homeostasis is the body’s way of keeping its internal environment stable despite changes.

Key Term: Homeostasis

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

When you eat food, it is broken down into glucose and dissolved in the bloodstream. Some of this is absorbed by cells to use for energy, and some is converted into glycogen, which is stored in the liver. Glycogen is an important storage form of glucose for the body and can be broken down into glucose when there is no food available.

The concentration of glucose in the blood needs to be within a certain range. The hormones insulin and glucagon keep glucose within this range, therefore maintaining homeostasis.

When blood glucose levels are high, insulin is produced by the pancreas to tell the cells of your body to absorb glucose. It also tells your liver to begin storing glycogen. This lowers glucose levels. When glucose is low, the pancreas produces glucagon to tell the liver to break down glycogen to release glucose. This raises glucose levels. The action of insulin and glucagon balance the levels of glucose. You can see this in Figure 5 below.

Key Term: Insulin

Insulin is a hormone that is produced by the pancreas and that is involved in regulating blood glucose levels.

Key Term: Glucagon

Glucagon is a hormone that is produced by the pancreas and that is involved in breaking down glycogen to release glucose into the blood.

Example 3: Understanding the Actions of Insulin and Glucagon on Blood Glucose Levels

The figure shows changes in blood glucose levels after a sugary drink.

  1. What hormone causes a decrease in blood glucose, shown as Q in the graph?
  2. What endocrine gland keeps the blood glucose concentration stable?
  3. What happens to the glucose when the blood concentration decreases at Q?
    1. It is broken down into glycogen.
    2. It is excreted in feces.
    3. It is taken up into cells.
    4. It is excreted in urine.

Answer

Part 1

Hormones are chemical messengers that travel through the blood to regulate different responses. They are secreted by endocrine glands, such as the pituitary gland, the adrenal glands, and the pancreas.

The hormones of the pancreas are involved in blood glucose homeostasis. Homeostasis is the maintenance of a constant, normal internal environment within an organism. The concentration of glucose needs to be within a certain range in our blood. Otherwise, it can be dangerous.

When you drink a sugary drink, the sugars are broken down into glucose and dissolved in the blood. Some of this glucose can be absorbed by cells in our body to provide energy. Some of the glucose can also be stored as glycogen in the liver. This can later be broken down into glucose when glucose levels are low.

After drinking a sugary drink and glucose is dissolved in the blood, the concentration of glucose increases in the blood. This causes the pancreas to produce insulin. Insulin causes the cells of the body to absorb glucose and also causes the liver to convert glucose to glycogen. In these ways, insulin lowers the blood glucose levels.

When blood glucose levels are low, the hormone glucagon is released by the pancreas. Glucagon can signal to the liver to start breaking down stored glycogen. This releases glucose and increases blood glucose levels.

You can see the actions of insulin and glucagon in the diagram below.

Therefore, the hormone insulin causes a decrease in blood glucose at Q in the graph above.

Part 2

Based on the explanation in part 1, the pancreas is the endocrine gland that keeps the blood glucose concentration stable.

Part 3

The concentration of glucose in the blood decreases at Q. This is because insulin causes the cells of the body to absorb glucose and also causes the conversion of glucose to glycogen in the liver. Normally, glucose is not excreted in the feces or in the urine.

Therefore, the blood glucose concentration decreases at Q because glucose is taken up into the cells.

The thyroid gland is located in the front neck area and consists of two lobes. In response to the pituitary gland being stimulated, the thyroid can produce thyroxine, which is involved in energy metabolism. Calcitonin is another hormone that is produced, which contributes to the regulation of blood calcium levels, for example by increasing calcium storage in bones. Embedded in the thyroid are four masses called parathyroid glands, which can secrete additional hormones. This is shown in Figure 6 below.

Key Term: Thyroxine

Thyroxine is a hormone that is produced by the thyroid gland and that is involved in energy metabolism.

Key Term: Calcitonin

Calcitonin is a hormone that is produced by the thyroid gland and that is involved in calcium homeostasis.

Have you ever felt nervous before going on stage, or before doing something new? This is because of the hormone adrenaline that is produced by the adrenal glands, which lie just above the kidneys.

Adrenaline is involved in the fight-or-flight response and can increase blood flow to muscles, increase the heart rate, dilate the bronchioles in the lung, and convert glycogen to glucose in the liver. All of this is to allow the body to expend more energy in order to respond to fearful or stressful situations. You can see the adrenal glands in Figure 7 below.

Key Term: Adrenaline

Adrenaline is a hormone that is produced by the adrenal glands and that controls the fight-or-flight response.

Example 4: Recalling the Function of Specific Hormones

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?

  1. Glucagon
  2. Adrenaline
  3. Insulin
  4. Testosterone
  5. Thyroxine

Answer

Hormones are chemical messengers that travel through the blood and have diverse functions. Some can be involved in reproduction, growth, homeostasis, and in response to danger.

Hormones are secreted by endocrine glands, such as the pituitary gland, the pancreas, and the adrenal glands. Each hormone has a specific target and function. Let’s look at some examples.

The hormones insulin and glucagon are produced by the pancreas and involved in regulating blood glucose levels. Glucose levels need to be within a certain range in order for the body to work at its best. You get glucose from breaking down the sugars in the foods you eat. Insulin is a hormone that acts to lower blood glucose levels, and glucagon can increase blood glucose levels.

The testes and ovaries can produce hormones involved in reproduction. For example, testosterone is produced by the testes and is involved in the development of secondary sex characteristics, like increased muscle mass in the male. This hormone is important for puberty.

Thyroxine is a hormone produced by the thyroid gland and is involved in energy metabolism.

The adrenal glands can produce adrenaline. This hormone is involved in the fight-or-flight response and has many functions, such as increasing blood flow to muscles, increasing the heart rate, dilating the bronchioles in the lung, and others. This is how our body prepares for a dangerous situation.

Therefore, hormone X is adrenaline.

The hormones discussed in this explainer and their functions are described in Table 1 below.

As shown in Table 1, the hormones produced by the endocrine glands have diverse functions. Some are involved in reproduction, growth, homeostasis, and response to danger. Some of them are more long lasting, like puberty, while others act more immediately, like insulin.

Example 5: Recalling the Activities of Endocrine Glands

The figure shows some different endocrine glands in the body.

  1. Which gland (A, B, C, D, or E) is not controlled by a pituitary hormone?
  2. Which gland (A, B, C, D, or E) produces calcitonin?

Answer

Part 1

Hormones are chemical messengers that travel through the blood and have diverse functions. Some can be involved in reproduction, growth, homeostasis, and response to danger. They are secreted by endocrine glands, such as the pituitary gland, the pancreas, the adrenal glands, the thyroid, the ovary and the testicles.

The pituitary gland can produce many hormones and can control the actions of other endocrine glands. This is why it is sometimes called the master gland.

The pituitary gland can act on the adrenal gland to produce adrenaline. This hormone is involved in the fight-or-flight response and prepares your body for a dangerous situation.

The pituitary gland can act on the thyroid to produce thyroxine. This hormone is involved in energy metabolism.

The pituitary gland can also act on the gonads (the testes and ovaries) to produce sex hormones like testosterone or estrogen. These hormones are involved in reproduction and are important during puberty.

The pancreas is not controlled by the pituitary gland, but it produces the hormones insulin and glucagon, which are involved in regulating blood glucose levels.

Therefore, the pituitary gland does not control the pancreas.

Part 2

Calcitonin is a hormone produced by the thyroid and is involved in calcium homeostasis.

Therefore, the thyroid is the endocrine gland that produces calcitonin.

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

Key Points

  • Hormones are chemical messengers that travel in the blood and 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 are growth hormone, prolactin, and oxytocin.
  • The testes can produce testosterone, and the ovaries can produce estrogen and progesterone.
  • The pancreas can secrete insulin and glucagon, which are involved in glucose homeostasis.
  • The thyroid can produce thyroxine and calcitonin.
  • The adrenal gland can produce adrenaline, which is involved in the fight-or-flight response.

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