General Adaptation Syndrome: Definition, Phases & Changes

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  • 0:01 General Adaptation Syndrome
  • 0:45 The Alarm Phase
  • 2:36 The Resistance Phase
  • 4:14 The Exhaustion Phase
  • 5:10 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

The general adaptation syndrome is a predictable series of phases related to stress. This lesson will explore some of the physiological and psychological changes associated with each phase.

General Adaptation Syndrome

Being called predictable is anything but a compliment. If I could predict your every move when playing a game like chess, then not only would you lose every time, but I would get bored really quickly.

Yet a person's, almost any person's, response to a stressor is quite remarkably similar and predictable. So much so that Hans Selye, an endocrinologist, coined a term known as the General Adaptation Syndrome (GAS), to describe a physiological response to a stressor that occurs in a specific sequence. The three phases of stress, and how your body changes with each phase, include the:

  1. Alarm phase
  2. Resistance phase
  3. Exhaustion phase

The Alarm Phase

When a person is first confronted with a stressor, something that brings about stress, they enter the first phase of the GAS. This first phase is known as the Alarm Phase.

During this immediate and involuntary phase, a hormone called epinephrine, also known as adrenaline, is released among plenty of other biochemical messengers.

These biochemicals cause lots of changes, including:

  • An increase of blood sugar, a.k.a. blood glucose. You know that drinking tons of sugar-laced soft drinks give you an energy rush. Your body tries to mimic this naturally by quickly releasing lots of sugar into the bloodstream from its energy stores. This energy supply is necessary during times of stress so you stay mentally alert and are ready to move, run, or fight at a moment's notice.
  • An increase in blood pressure, heart rate, and respiratory rate so you get lots of oxygen and blood delivered to your important organs and muscles - muscles like skeletal muscles, the muscles that help you run, like your quads, and fight, like your triceps.
  • A concurrent decrease in blood flow to the skin and digestive organs because they're irrelevant in a fight or flight response, such as that found during the alarm stage. The last thing your body wants to do when under duress is give precious resources, like blood that's filled with oxygen and sugar, to organs that will not help you immediately fight off a stressor or flee from it. What are you going to do, eat a picnic and digest some food while a bear is charging at you? I don't think so! And neither does your body.

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