What is stress? Stress is a physical and psychological response to demands or challenges, known as stressors, that are perceived as threatening or exceeding an individual's ability to cope.
Stress can originate from a variety of sources, and can be divided into two major categories - physical stressors and psychosocial stressors.
Physical stressors are related to the environment, bodily functions, or physical events that place a strain on the body. These stressors can influence physiological processes and may require the body to aadjust or adapt in response. Examples of physical stressors include extreme temperature, injury or illness, noise, sleep deprivation, poor nutrition. Stressors can be acute, such as sudden illness or a job interview, or chronic, like ongoing financial worries or long-term health problems. Physical stressors require an immediate bodily reaction via reflexive mechanisms involving activation of the brain stem and the hypothalamus, therefore generating a rapid activation of the autonomic nervous sytem and HPA axis.
On the other hand, psychosocial stressors are related to one's psychological perception of their social environment and interpersonal relationships. These stressors involve the demands placed on indiiduals in their roles in society and how they interact with other people. Examples of psychosocial stresors include workplace challenges, financial problems, grief and loss, major life changes, social isolation, family and relationship issues. Psychosocial stress are first evaluated and processed in the frontal lobes and thalamus, generating cognitive appraisals that trigger stress reesponses via connections of the prefrontal cortex with the limbic structures. (and HPA?)
There are two major stress-response systems in our body. The Sympathetic-Adrenal-Medullary axis and the Hypothalamic-Pituitary-Adrenal axis. They both are activated by stress, but they operate differently and have different roles in the stress response.
The SAM axis is part of the autonomic nervous system, and functions to rapidly response to stress. This axis is the first and fast response of the body, mobilizing energy and resources to deal with threatening situations. Here is how it works:
- When the brain perceives a stressful situation, the hypothalamus is activated and suppresses the parasympathetic nervous system while simultaneously activate the sympathetic nervous system, leading to the stimulation of the adrenal medulla (the inner part of the adrenal glands, located on top of the kidneys).
- The adrenal medulla then secretes catecholamines, adrenaline (epinephrine) and noradrenaline (norepinephrine) into the bloodstream. These hormones prepare the body for a "fight or flight" response, which includes increasing heart rate, elevating blood pressure, dilating airway, redirecting blood flow to muscles, increasing metabolism, and dilating pupils.
Hypothalamic-Pituitary-Adrenal (HPA) axis is the secondary stress response, implicating with the release of cortisol, therefore will have more enduring effects in the body:
- The hypothalamus is activated and releases corticotropin-releasing hormone (CRH),
- CRH will activate the sympathetic nervous system, triggering the behavioural fight-flight response.
- Then, CRH stimulates the pituitary gland to produce and release adrenocorticotropic hormone (ACTH) into the bloodstream.
- ACTH then prompts the adrenal cortex (the outer part of the adrenal glands) to produce and release cortisol, a glucocorticoid hormone.
- Cortisol will then exert a number of effects in the body, such as temporary increase in energy via gluconeogenesis in the liver, preparing it even further for a fight-or-flight response.
Cortisol works more slowly than the catecholamines, affecting many parts of the body to maintain homeostasis and provide a sustained response to stress. It increases glucose in the bloodstream, enhancese the brain's use of glucose, and increases the availability of substances that repair tissues
Cortisol also has a negative feedback effect on both the hypothalamus and pituitary gland, which serves to modulate the response and eventually shut down the HPA axis when cortisol levels are high enought and the stressor is no longer present.
The formation of stress involves several key components. First, an individual perceives something as a challege or threat. This perception can vary widely among individulas; what is stressful for one person may not be for another. The brain assesses the stressor in terms of potential threat and determines whether personal resources are sufficient to meet the demands of the situation. This appraisal process is crucial and can determine the intensity of the stress response. If the situation is appraised as threatening and exceeding one's resources, the body's stress response is activated. This involves a series of physiological changes designed to improve an individual's ability to cope with the stressor. Common changes include increased heart rate and blood pressure, tense muscles, quickened breathing, and heightened senses. Individuals may respond to stress with various behaviours, ranging from agression and anger to withdrawal and anxiety. These behaviours are attempts to deal with the stressors, either by confronting it or by avoiding it. Ideally, once the stressor is managed or removed, the body's stress response systems will return to baseline levels, a process known as homeostasis.
If the stressor persists or the individula is unable to adapt effectively, the stress response can become chronic, leading to wear and tear on the body. Chronic stress can lead to various negative health outcomes, including mental health disorders like anxiety and depression, cardiovascular disease, obesity, diabetes, and gastrointestinal problems, among others. Therefore, managing stress through strategies such as exercise, social support, and professional therapy is crucial for maintaining overall health and well-being.
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