Stress and Gut Brain Axis

Stress: a state of physical or mental arousal produced by external stressors that an individual finds challenging or incapable of dealing with

• subjective perception and experience of tension that results from trying to adjust or cope with change

The components of stress:

1. Stressor- a stimulus, object, or event that evokes arousal

2. Stress- physical or mental tension caused by a stressor

3. Stress response- a physiological or psychological reaction to the stressor/stress

Sources of stress:

• stress can be the result of external environmental pressures or internal, psychobiological ones

• how we perceive and respond to stress is subjective and different for everybody but the automatic physiological response is the same

Internal vs. External Stressors:

Mental health is influenced by internal and external factors.

Internal:

• Biological (genetic inheritance, neurotransmitter or hormonal activity, substance use, stress response etc)

• Psychological (attitudes, beliefs, decisions, emotions, learning and memory)

External:

• Social (interpersonal relationships, family, friends, cultural traditions, support network etc)

• Environmental (poverty, pollution, access to community services and natural resources)

Acute vs. Chronic Stress

Acute stress (short term)- a state of brief but intense physiological arousal in response to an immediate perceived stressor that normally has no negative effects on health and well being

• can be beneficial and exciting as it motivates and energises us to cope

Chronic stress (long term)- prolonged physiological arousal in response to a persistent stressor that negatively affects health and wellbeing

• often sneaks up on us as it is less intense but more gradual and continuous, hence we become accustomed to feeling uneasy, upset or hopeless

Eustress vs Distress

The two types of stress:

• Eustress: a positive state of arousal that energises and helps the body perform at optimal levels

• Distress: a negative state of arousal that drains energy and reduces performance levels

Stress and Performance

• stress can be beneficial or detrimental depending on the amount of arousal

• too little stress = poor attention and motivation

• too much stress = overwhelmed/ burnout

Psychobiological process

To understand stress, researchers usually adopt a ‘psychobiological approach’ which takes into consideration the interaction of physiological factors and psychological (cognitive, perceptual and emotional) factors these can contribute to and also alleviate stress

Stress: as a biological process

• stress results in physiological changes in the body, specifically due to the activation of the sympathetic division of the autonomic nervous system

• often stressors arouse our survival instincts, pumping us full of energy to either confront the threat or escape and avoid it

Fight-Flight Response:

• Without conscious awareness, our body automatically and involuntarily responds to perceived threats (stressors) by preparing itself to confront/fight or escape/take flight so that it can increases it’s chances of survival

• this process is instant but only last a small amount of time

• within milliseconds, the sympathetic N.S stimulates the hypothalamus which activates the adrenal glands to secrete “stress hormones” - adrenaline and noradrenaline into the bloodstream which activate the organs (heart, lungs, liver and kidneys)

Some physiological responses to stress that are designed to prime the body for action:

• Adrenaline released

• heart rate increases to pump more blood around the body

• respiration increases oxygen supply

• pupils dilate to let more light in to see better

• muscle tension increases for strength and agility

• unnecessary functions (digesting, sex drive) are suppressed

After Fight or Flight

• once the threat is removed the parasympathetic nervous system kicks in to calm the body and restore an equilibrium

• However, if we believe there is no hope of defeating the threatening stressor, our body may start to shut down, but this is rare

• our sympathetic nervous system becomes activated but our parasympathetic nervous system becomes dominant over the top of it

• this switches off our responses to a point of TONIC IMMOBILITY (we freeze up)

• like having your foot on the accelerator with the park brake on

Freeze Response

• the freeze response is the body’s last line of defense

• the body collapses and releases opiate receptors to have a numbing effect

• this reduces pain sensation and conscious awareness

• this can spare us from remembering the traumatic experience

• the parasympathetic n.s dominates but the sympathetic n.s is also activate causing the body to freeze, like the accelator is getting pushed down when the park brake is on

Fight/Flight/Freeze

• Fight/Flight: autonomic sympathetic n.s dominates (Arousal for survival)

• freeze: autonomic parasympathetic n.s dominates (shuts down for survival)

The role of cortisol

• cortisol is a steroid hormone released by the adrenal gland to help maintain daily homeostasis

• cortisol levels are usually highest in the morning and lowest at night

• meaning they decrease over the day

• increased cortisol levels activate our sympathetic n.s fight-flight response

• cortisol is able to metabolise glucose to release more energy to take action and increase our chances of survival

• when the threat is removed, cortisol levels drop to return to our physiological systems normal state

• if the threat is not removed and intense stress continues over a prolonged time, too much cortisol remains in the bloodstream, which can lead to a biochemical imbalance which can have severe negative impacts

• called the “stress” hormone, if you have high levels of cortisol in blood stream (quantitative and objective data) it indicates high levels of stress

Negative effects of excess cortisol:

• weakened immune system= more vulnerable to infection and disease

• sleep disturbances and chronic fatigue

• decreased metabolism and high blood sugar

• weight gain and decreased bone density

• impaired cognitive functions

• anxiety and depression

ENTERIC NERVOUS SYSTEM:

Communication between your brain and your gut = the gut-brain axis

• “butterflies” in your stomach

• cravings for comfort food

• a gut-feeling about something

The Enteric Nervous System (E.N.S) is a division of your autonomic/peripheral nervous system. The connection between the brain and the E.N.S contain both sensory (afferent) and motor (efferent) neurons. Its role is to:

• coordinate the rhythmic muscles contractions that move materials (food) along the gastrointestinal tract

• regulate gastric acid secretion

• regulate bodily fluids and blood flow

• regulate the release of gut hormones and neurotransmitters

• interact with the immune system and central nervous system

• coordinate immune and defence responses (against toxic foods and bacteria)

The Vegus Nerve:

• one of the body’s biggest nerves and faciliates between the CNS and ENS

• it is bidirectional, info can be sent to and from gut

Originates in the brain stem and extending to colon, it connects the brain to organs of the autonomic nervous system via nerve fibres that directly link to:

• Pharynx (where swallowing happens)

• Larynx (voice box) and trachea (windpipe)

• oesophagus

• heart and lungs

• stomach

• pancreas, kidney and gall bladder

• small and large intestines

• rectum

The Vegus Nerve controls many bodily functions including:

• digestion

• heart rate

• immune response

• mood (stress and anxiety)

Communication along The Vegus Nerve is BIDIRECTIONAL (neural signal goes both ways)

• Sensory/afferent messages from the gut to the brain

• Motor/efferent messages from the brain to the gut

90% of vegus nerve fibres are afferent, sending sensory messages from the gut to the brain e.g

• movement of the gastrointestinal tract muscles

• tension in muscles

• level of fullness (empty or bloated)

• pain

• information about hormones, neurotransmitters and other chemical signa;s

10% of vegus nerve fibres are efferent, transmitting motor messages from the brain to the gut

e.g

• release of saliva and bodily fluids

• signals about incoming food (from taste and smell)

• required changes in the GI tract to aid digestion

• messages about fight/flight/freeze response and the return of systems to homeostasis

The Gut Brain Axis

• The GBA provides bidirectional communication between the CNS and ENS

• it contains direct and indirect pathways between the gastrointestinal tract and the cognitive and emotion areas of the brain

• when we feel stressed or anxious we may experience an upset stomach due to the signals sent from the brain to the gut

• similarly, disruptions to the functioning of our gut (GI tract) may affect our mood, motivation, emotional arousal, behaviour and cognitive processes

Microbiomes and Microbiota

Microbiome= gut environment (home); the population of microbiota

Microbiota= organisms such as bacteria, viruses and fungi

• the GI tract is a dynamic system of almost 100 trillion bacteria and 1000 different microbe species

• Microbiota helps the GI tract to function optimally but can be affected by internal and external factors such as diet, disease, lifestyle, stress etc.

Characteristics of an optimal gut microbiome include:

• The number of different species

• The diversity of different species

• Their resistance to change over times

These characteristics decrease with age, making us more susceptible to stress and illness over time

Dysbiosis

• occurs when there is less diversity of healthy microbiota and there is no longer a healthy balance of bacteria in the microbiome/GI tract

• such imbalance and lack of diversity can cause a range of digestive issues and impact the overall effectiveness of the immune system

• Emerging research also suggests that this imbalance or lack of diversity can impact psychological processes such as: cognitive functioning, mood, increased stress and anxiety

Social Behaviour:

• mor

Stress and Gut Microbiota

GBA is an emerging field of research

• most studies so far have been on animals but recent, promising ones have been done on humans

Research shows that chronic stress (hence increased cortisol levels impact:

• the diversity of healthy microbiota

• psychological processes and behaviour

• high levels of stress + increased cortisol levels = changes to gut microbiota associated with anxiety and depression

Due to a reduction of “good” bacteria and diversity in the microbiome, stress may affect different functions of the GI tract including:

• changes in blood flow, gastric secretions and gut motility

• increase in visceral perception (increased sensitivity to gut movements and processes)

• intestinal permeability (greater leakage through gut lining)

• negative affects of gut microbiota

GBA and Stress Summary

• a healthy microbiome with the right type of diverse

• a balanced microbe population in our gut can help people cope better with stress

• abnormal microbiota reduces resistance and increases susceptibility to stress related disorders (physiological and psychological)

• likewise, stress can disrupt the health of the gut microbiome (it is bidirectional)

• treatment with healthy microbiota can reduce stress responsiveness and anxiety related behaviour