What is Serotonin? - Definition & Function

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  • 0:00 Definition of Serotonin
  • 0:44 The Uses of Serotonin
  • 2:49 Serotonin Syndrome
  • 3:28 Other Ways to Affect Serotonin
  • 4:14 Lesson Summary
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Lesson Transcript
Instructor: Laura Gray

Laura has taught at the secondary and tertiary levels for 20+ years and has a Ph.D. in Instructional Design for Online Learning.

This lesson describes what serotonin is and how it is used in the body. In addition, we'll discuss SSRIs, which boost serotonin levels in the brain; side effects of using SSRI's; serotonin syndrome; and natural ways to boost serotonin in the body.

Definition of Serotonin

Serotonin is a chemical that is manufactured in the body and acts as a neurotransmitter. A neurotransmitter is a chemical that helps signals cross from one neuron, or nerve cell, to the other. Although most people who have any knowledge of serotonin know that it is one of the brain chemicals responsible for regulating people's moods, what many people don't know is that 80-90% of serotonin is manufactured and lives in the gastrointestinal tract, or in short, our digestive system! So, even though it is widely believed to be a 'brain chemical,' serotonin lives primarily in our stomach and intestines, where it helps to regulate gastric functions.

The Uses of Serotonin

Serotonin was discovered by Maurice Rapport in 1948, so it's relatively 'new' in terms of what we know about it. It is widely believed by the medical community, though, that serotonin is definitely responsible to help regulate our moods, social behavior, appetite and digestion, sleep, memory, and sexual function. Therefore, it has a wide variety of functions that keep humans happy and on track.

The biggest news about serotonin that you've probably heard is its relationship to depression. While there is an almost-certain link between the two, what scientists don't know is if low levels of serotonin in the brain cause depression, or if depression causes lower levels of serotonin. Nobody knows for sure. What scientists and doctors do know, however, is that selective serotonin reuptake inhibitors, or SSRIs for short, are a type of drug that can help tremendously with depression in many people.

Unfortunately, scientists don't know exactly why these particular drugs work. Despite this, SSRIs are the most widely prescribed type of antidepressants in the world and are approved by the Food and Drug Administration (FDA) specifically to treat depression. One thing that is known, however, is how SSRIs work. Under normal circumstances, serotonin transmits its neural information from neuron to neuron in the brain, and then it is reabsorbed by the body. When a patient is taking SSRIs, however, the reabsorption by the body is prevented, so the amount of serotonin in the brain increases. This is thought to cause the patient to feel better and less depressed. Interestingly, the drugs MDMA and cocaine work the same way, which is what causes users to feel high.

SSRIs, as with any type of drug, can cause side effects when taken. The following side effects may be a result of more serotonin being produced:

  • Diarrhea
  • Dizziness
  • Agitation
  • Dry mouth
  • Headaches
  • Loss of appetite
  • Loss of sex drive
  • Insomnia
  • Nausea or vomiting
  • Weight gain or weight loss

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