The Mechanisms of Hormone Action

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  • 0:01 Hormones
  • 1:14 Activation
  • 2:10 Transport
  • 3:07 Target Cells
  • 3:51 Secondary Messengers
  • 5:00 Lesson Summary
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Lesson Transcript
Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

To keep everything regulated, your body constantly needs to send messages to different cells. It does this by using hormones. In this lesson we'll look at how hormones work and what they do.


In 1860, three men named William Russell, Alexander Majors and William Waddell founded a revolutionary message delivery system called the Pony Express. By using young riders who would continually change horses, they were able to deliver mail from Missouri to California in exactly ten days which, at the time, was simply mind blowing. The Pony Express represented an idea that our bodies understand very well. A reliable message delivery system is crucial to maintaining a complex system. You need to send messages quickly and precisely. Now, our bodies may not have miniature horse riders, but we do have hormones, molecules that send messages that impact other cells. Hormones are how our body regulates growth and development and maintains homeostasis, or the balance of chemicals in the body. When something needs to happen, hormones are sent out from the glands of the endocrine system to send the message to the other cells. It's a tough job, but as the messengers of the Pony Express swore, the mail must go through.


Let's start at the beginning. How are hormones activated? Well, there are three different kinds of stimuli that tell endocrine glands to start releasing hormones. First is humoral, or blood levels. When certain glands detect an irregular level of ions or nutrients in the blood, they send out hormones to tell other cells how to correct this. The next set of stimuli are neural, meaning from the central nervous system. Although most of this process is separate from the nervous system, the brain can send out signals telling endocrine glands to create hormones under certain situations, like if you're really stressed. The third set of stimuli to release hormones are actually hormonal, or hormones received by an endocrine gland. Whatever the stimuli is, this signal tells the gland what the problem is and how to fix it. Then hormones are sent to deliver the message.


So, once the endocrine gland receives a signal, it's time to release the hormones and how this is done depends on where they're going. We've got three main kinds of actions taken by hormones. First are autocrine actions, where the hormone delivers the message to the cell that produced it. The hormone is excreted out of the cell then comes back in, causing the message to be delivered. The next option is a paracrine action, or message delivery to a neighboring cell. This is pretty simple and just involves the hormone leaving the producing cell and pretty much already being at its destination. The final option is an endocrine action, the delivery of hormones to distant cells. These are the long haul messengers. They enter the bloodstream via the capillaries and travel all across the body delivering messages.

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