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13.24: Hormones

Difficulty Level: At Grade Created by: CK-12
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Steroid hormones. How do they work?

As hormones, they are the messengers of the endocrine system. Obviously they must change something in the cell.

How Hormones Work

Hormones are the messenger molecules of the endocrine system. Endocrine hormones travel throughout the body in the blood. However, each hormone affects only certain cells, called target cells. A target cell is the type of cell on which a hormone has an effect. A target cell is affected by a particular hormone because it has receptor proteins that are specific to that hormone. A hormone travels through the bloodstream until it finds a target cell with a matching receptor it can bind to. When the hormone binds to a receptor, it causes a change within the cell. Exactly how this works depends on whether the hormone is a steroid hormone or a non-steroid hormone. At the link below, you can watch an animation that shows how both types of hormones work. http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP13704

Hormones are discussed at http://www.youtube.com/watch?v=HrMi4GikWwQ&feature=related (2:28).

Steroid Hormones

Steroid hormones are made of lipids, such as phospholipids and cholesterol. They are fat soluble, so they can diffuse across the plasma membrane of target cells and bind with receptors in the cytoplasm of the cell (see Figure below). The steroid hormone and receptor form a complex that moves into the nucleus and influences the expression of genes. Examples of steroid hormones include cortisol and sex hormones.

A steroid hormone crosses the plasma membrane of a target cell and binds with a receptor inside the cell.

Non-Steroid Hormones

Non-steroid hormones are made of amino acids. They are not fat soluble, so they cannot diffuse across the plasma membrane of target cells. Instead, a non-steroid hormone binds to a receptor on the cell membrane (see Figure below). The binding of the hormone triggers an enzyme inside the cell membrane. The enzyme activates another molecule, called the second messenger, which influences processes inside the cell. Most endocrine hormones are non-steroid hormones, including insulin and thyroid hormones.

A non-steroid hormone binds with a receptor on the plasma membrane of a target cell. Then, a secondary messenger affects cell processes.


  • Hormones work by binding to protein receptors either inside target cells or on their plasma membranes.
  • The binding of a steroid hormone forms a hormone-receptor complex that affects gene expression in the nucleus of the target cell.
  • The binding of a non-steroid hormone activates a second messenger that affects processes within the target cell.

Practice I

Use this resource to answer the questions that follow.

  • http://www.hippocampus.org/Biology \begin{align*}\rightarrow\end{align*} Biology for AP* \begin{align*}\rightarrow\end{align*} Search: Mechanisms of Hormone Actions
  1. What is a hormone receptor?
  2. Describe two different types of cell-surface hormone receptors.
  3. What is a G-protein coupled receptor?
  4. What is a second messenger? Give an example. What would be the first messenger?
  5. What is an intracellular receptor?
  6. Describe the structure of an intracellular receptor.
  7. How do intracellular receptors function?

Practice II


1. Define hormone.

2. Compare and contrast how steroid and non-steroid hormones affect target cells.

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A chemical messenger molecule.

non-steroid hormone

Hormone made of amino acids; cannot diffuse across the plasma membrane of target cells; binds to a receptor on the cell membrane.

receptor protein

Protein with a binding site for a particular hormone or other molecule.

second messenger

Molecule which influences processes inside the cell; activated by a process initiated by the binding of a non-steroid hormone to its receptor.

steroid hormone

Fat soluble hormone made of lipids, such as phospholipids and cholesterol; can diffuse across the plasma membrane of target cells and bind with receptors in the cytoplasm

target cell

Type of cell on which a particular hormone has an effect because it has receptor molecules for the hormone.

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At Grade

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Date Created:
Feb 24, 2012
Last Modified:
Aug 17, 2016
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