Psychology: Physiological Stress Responses

Stress

A psychobiological response produced by internal or external stressors.

Stressor

Any stimulus that causes stress. A stressor can be a physical stimulus (loud noise, heavy object, intense light, etc.) or psychological in nature (failing an exam, running late to class etc.).

Internal Stressor

Originates within the individual; e.g. a personal problem that causes worry about future circumstances or the experience of pain that may be perceived as signalling a serious illness (mental).

External Stressor

Originates outside the individual from situations and events in the environment; e.g. having too much homework, being a victim of crime, stuck in traffic (physical).

Acute Stress

Stress that lasts for a relatively short time and is specific to the demands of a particular situation.

Chronic Stress

Stress that continues for a prolonged period of time. This can occur in circumstances such as ongoing financial difficulties, social isolation and loneliness, relationship problems, long-lasting health problems, etc.

Fight, Flight or Freeze

An involuntary and acute stress response, involving physiological changes produced by the sympathetic nervous system.

Fight

Confronting and fighting off a threat.

Flight

Escaping by running away to safety.

Freeze

keeping absolutely still and silent to avoid detection.

First Part of Stress Response

- stress is experienced and detected by the amygdala which sends a signal to the hypothalamus.
- hypothalamus responds to the stressor by activating the sympathetic nervous system which then stimulates the adrenal medulla
- adrenal glands secretes adrenaline and noradrenaline into the blood stream
- the hormones activate various organs that prepare the body for action

Second Part of Stress Response

- hypothalamus stimulates nearby pituitary gland to initiate the HPA axis to secrete additional stress hormones (mostly cortisol)

Adrenaline

A hormone secreted during stress. It prepares the body for action. Often involved with acute stress.

Cortisol

Cortisol is a primary stress hormone secreted in response to an acute stressor and a chronic stressor. It is slower acting compared to other stress hormones but longer lasting. This allows the body to deal with stress for a longer period.

Effects of Cortisol

- increasing blood glucose for energy
- enhancing metabolism
- turns off bodily systems not required to deal with stressor (reproductive functions)
- anti-inflammatory effect, blocking white blood cells that contribute to inflammation
- slows wound healing

Healthy Stress Response

Characterised by a quick rise in cortisol levels, followed by a rapid decline with the termination of the stressful event.

Consequences of Prolonged Stress

- impaired immune system (vulnerability to disease)
- weight gain
- colds, flu, hypertension, digestive problems, atherosclerosis, high blood sugar levels & diabetes
- impaired cognitive performance, learning problems, impaired memory formation, depression, PTSD & other anxiety disorders

Gut Brain Axis

A bidirectional (two-way) communication link between the central and enteric nervous systems, linking cognitive and emotional areas in the brain with the gastrointestinal tract.

Vagus Nerve

Responsible for the communication between the gut and the brain. It is the longest nerve in the body, running from the brain stem to the intestines.

Vagus Nerve Fibres

90% of vagus nerve fibres are afferent (sensory) connections that sends signals up from the gut to the brain. The remaining 10% are efferent (motor) connections.

Microbiota

Refers to the highly diverse and dynamic system of bacteria and micro-organisms that live in the human gastrointestinal tract. The collective term is microbiome. Microbiota can be influenced by diet, infection, disease and lifestyle choices.

Microbiota and Neurotransmitters

Gut bacteria help produce dopamine, GABA and over 80% of the body's serotonin. Disturbances in microbiota can change the production of neurotransmitters in the gut.

Enterotype

A term used to describe each individual's personal composition of microbiota.

Gut Dysbiosis

Refers to the imbalance or lack of diversity in gut bacteria. Gut dysbiosis can reduce the effectiveness of the immune system, cause illnesses and influence the effects of neurotransmitters.

Gut Dysbiosis can cause

- mood disorders
- changes in the production of neurotransmitters in the gut (dopamine, GABA, serotonin)
- digestive disorders
- stress reactivity
- heart disease
- mental health disorders

Selye's General Adaptation Syndrome (GAS)

A three stage physiological response to stress that occurs regardless of the stressor that is encountered. This means that GAS is non-specific and will occur regardless of the source of stressor.

Stages of GAS

alarm (shock/countershock), resistance, exhaustion

Alarm Reaction Stage

The first stage of GAS that occurs when the person first becomes aware of the stressor. This stage involves the shock and countershock stage.

Shock Substage

The body goes into temporary shock and its ability to deal with the stressor falls below normal level. The body reacts as if were injured (e.g. decrease in body temp, blood pressure and muscle tone). The countershock stage combats this.

Countershock Substage

Activates the sympathetic nervous system, triggers fight or flight and increases the body's resistance to the stressor. Adrenaline, noradrenaline, cortisol and other stress hormones are released into the bloodstream. Heart and respiratory system accelerate and muscles are supplied with more energy (glucose & oxygen).

Resistance Stage

If stressor isn't dealt with immediately, the body will enter the resistance stage. It's resistance to the stressor rises above normal but arousal of the alarm reaction stage diminishes through the parasympathetic nervous system. Physiological processes not required to deal with stress decrease.

Cortisol in the Resistance Stage

Cortisol remains in the bloodstream to energise the body and acts as an anti-inflammatory agent and provides fast-acting pain relief. The ability to adapt to the specific stressor increases, but leaves the immune system weak to diseases and illnesses.

Exhaustion Stage

If the stressor isn't dealt with during the resistance stage, the body will enter exhaustion. Alarm reaction changes may reappear but the body cannot sustain resistance against it. As the body has been dealing with the stressor for a long time, stress hormones have been depleted and the immune system becomes vulnerable to mental and physical disorders.

Effects of Exhaustion Stage

- fatigue
- sleep disturbances
- irritability
- crying spells
- hypertension
- permanent changes to body organs

Strengths of GAS

- extended findings on the fight-flight response
- further understanding between stress and disease
- identifies biological processes associated with body's stress response
- explanation of the potentially detrimental effects of exposure to persistent stress proven by further research

Limitations of GAS

- assumes everyone has the same responses to any stressor, does not explain individual differences
- does not account for cognitive aspects of the stress response
- based on animal research, limited relevance to human stress response
- not all experience the same physiological reactions to chronic stress