Hormones

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Hormone Objectives

Describe what hormones are, including how they travel through the body and impact target cells.
List the hormones produced by various endocrine organs.
Explain how thyroid hormone and parathyroid hormone regulate blood calcium levels.

Hormones are molecules that cause cells to do something. When you think of a hormone, there are some familiar names like testosterone, estrogen, or growth hormone. All of these are chemicals that are released by cells that cause other cells to make products, grow, divide, or perform a number of other functions.

Most people assume that the nervous system does most of the controlling of body functions. However, hormones from endocrine cells also have significant impact as we will see in this section.

Understanding hormones is so critical within the endocrine system, we are beginning this section by reiterating some of the messages from the previous section (webpage) and introducing examples of hormones and their functions.

Many hormones have opposing actions and this video provides examples.

Hormones impact target cells that have specific receptors on their plasma membranes. The effects differ depending on the type of hormone.

The two figures below demonstrate that hormones cause a complex cascade of responses within a target cell. These responses can vary from increased production to decreased activity, depending on the hormonal trigger. Research is ongoing into the array of possible hormonal responses.

Thyroid

The thyroid and parathyroid glands are both located in the neck.

The pituitary increases thyroid activity by releasing thyroid-stimulating hormone. The thyroid produces different hormones, including calcitonin.

Parathyroid glands on the surface of the thyroid produce parathyroid hormone.

Calcitonin and parathyroid hormone have opposing actions intended to maintain blood calcium homeostasis.

Besides the bones, which organs have target cells for calcitonin and parathyroid hormone?

This is a closer look at the thyroid, including cells arranged in follicles full of colloid.

The thyroid and parathyroids not only produce different hormones, they are also structured very differently.

The thyroid gland can develop a variety of disorders. This video describe three of the most common thyroid diseases.

Thyroid hormone medications are the most prescribed medications in the United States, even higher than statins to lower cholesterol or blood pressure medications. At first that may seem like we have an epidemic of thyroid problems. However, part of the issue is that thyroid hormone levels vary significantly from person to person, and it is hard to determine what is “normal.” Many people use thyroid hormones as a way to raise metabolism with the goal of losing weight. There are risks associated with this. Elevating thyroid hormones can increase stress, agitation, and have long-term impacts on organ health.

Thyroid follicles filled with colloid

Endocrine cells form tissues that are distinctive from one organ to the next.

Endocrine glands within organs differ from exocrine glands. An endocrine gland is a collection of endocrine cells that secret hormones into the ____ that then carries those hormones to target cells. Exocrine glands secrete their substances through a tube, often out to the surface of the organ. Is a sweat gland an example of an endocrine gland or an exocrine gland? ___

So far, we have examined the pituitary (anterior and posterior), thyroid gland, and parathyroid glands.

Examine this figure, and for these endocrine organs, list the hormones they produce:

Pancreas

Adrenal Glands (2)

Testes (2)

Ovaries (2)

Put together the information from this section and the previous page to identify these endocrine organs, determine their locations, and list the hormones they produce.

The next section explores how hormones relate to stress.

Check your knowledge. Can you:

Describe what hormones are, including how they travel through the body and impact target cells.
List the hormones produced by various endocrine organs.
Explain how thyroid hormone and parathyroid hormone regulate blood calcium levels.