The term “stress” is colloquially used to refer to real or perceived challenging situations that threaten an individual’s stability or homeostasis (state of equilibrium). Such situations may be referred to as stressors, while the reaction of the body to the stressor is referred to as the stress response. Acute activation of the stress response is beneficial since it helps the individual cope with a situation by either overcoming or avoiding the stressful situation. However, prolonged activation of the stress response can be detrimental, having an adverse impact on every system of the body.
Some of the physical effects of chronic stress include an increased risk of:
- Cardiovascular disease
- Type-2 diabetes
- Digestive disorders
Table of Contents
Central Nervous & Endocrine Systems
The stress response is characterized by the activation of the hypothalamic-pituitary-adrenal axis. The emotional centers of the brain activate the hypothalamus which results in the secretion of hormones from the pituitary gland and the activation of the sympathetic nervous system.
The sympathetic nervous system is involved in the fight-or-flight response. The fight-or-flight response is mediated by the release of epinephrine (adrenaline) from the adrenal glands and the direct activation of the peripheral autonomic nerves. The fight-or-flight response involves increased heart rate and blood pressure, increased rate of respiration, increased release of glucose from the liver and the activation of muscles in the arms and legs. This readies the body to deal with a life-threatening emergency.
The hormones released by the pituitary gland during a stress response signal the adrenal glands to release the hormone cortisol. Cortisol helps to keep the body in an alert state to respond to stressors by keeping the sympathetic nervous system activated. Cortisol also plays an important role in suppressing the initial stress response after the disappearance of the stressor and achieving homeostasis. For example, cortisol is key in replenishing energy stores in the body that become depleted during the stress response. The activation of the sympathetic nervous system and elevation of cortisol levels are necessary for mediating an effective response to acute stressors. Prolonged exposure to stress leads to the dysfunction of the brain regions that mediate response to acute stressors.
Acute stress increases blood supply to the brain and improves learning and memory, whereas chronic stress impairs learning and memory. Chronic stress also leads to changes in various regions of the brain that result in increased activity in emotional regions of the brain and decreased activity in brain regions involved in complex intellectual tasks, like the frontal cortex. Consistent with those changes, chronic stress is associated with an increased risk of anxiety and depression and lower impulse control.
During acute stress, the fight-or-flight response produced by the activation of the sympathetic nervous system results in the diversion of energy to the brain and muscles. This means reduced energy is invested in activities like food intake and digestion and this may result in reduced appetite. Acute stress also results in reduced contractions of the muscles present in the digestive tract, as well as decreased gastrointestinal secretions.
Some of the common acute effects of stress on the gastrointestinal system include:
- Stomach pain
The release of cortisol following this initial fight-or-flight response results in increased appetite, and the intake of calorie-dense foods, such as foods rich in fats and sugars. Such stress-related indulgence in comfort foods helps to dampen the activity of circuits involved in the stress response. Since chronic stress often involves multiple stressful episodes over a day, there may be multiple instances of elevated cortisol levels and stress eating. This can result in increased food intake and obesity. However, in some cases, chronic stress can result in appetite and weight loss.
Chronic stress is also associated with an increased risk of type-2 diabetes. Chronic stress can result in increased motility and responsiveness of the gut during stressful situations. Chronic stress can thus contribute to the development of gastrointestinal conditions like inflammatory bowel disease and inflammatory bowel syndrome.
The activation of the sympathetic nervous system during acute stress increases heart rate and blood pressure. This is advantageous during exposure to stressors since this results in greater blood supply, and thus more oxygen and glucose, being delivered to the body’s tissues. However, chronic stress can lead to a long-term elevation in blood pressure that can cause cardiovascular conditions such as arrhythmias, myocardial infarctions (heart attack), cardiac arrest and stroke.
Chronic stress or recurring acute stress can result in wear and tear of the endothelial tissue that forms the inner lining of arteries. This leads to an inflammatory response and the formation of plaque. Cholesterol and fats tend to accumulate on this inflamed plaque and can restrict blood flow. This plaque can cause blood clots and block the supply of blood and oxygen to the tissue. Atherosclerosis refers to such a narrowing of arteries due to the formation of plaque. Atherosclerosis can cause chest pain, myocardial infarction, stroke and kidney failure, depending on the arteries affected.
Acute stress results in the activation of the fight-or-flight response to combat life-threatening situations or other emergencies. This requires greater blood and concomitant oxygen supply to organs to facilitate the flight-or-flight response. Acute stress thus involves activation of the sympathetic nervous system to increase the heart and breathing rate. Acute stress can cause hyperventilation, shortness of breath and even panic attacks in some cases. Chronic stress can worsen the symptoms of pre-existing respiratory conditions like asthma and chronic obstructive pulmonary disease (COPD) that includes chronic bronchitis and emphysema.
Acute stress causes muscles to tense up to protect them from injury and relax upon the overcoming or the disappearance of the stressor. However, in the case of chronic stress, muscles tend to remain tense for a prolonged period. Chronic stress may thus result in body aches including shoulder, neck and back pain. Furthermore, migraine and tension-type headaches may occur due to the tensing of the neck and scalp muscles.
The association between stress and illness has been recognized for many decades, with chronic stress resulting in suppression of the immune system. These immunosuppressive effects of chronic stress are responsible for increased susceptibility to infections. In contrast, acute stress results in the enhancement of the immune response. The immune-enhancing effects of acute stress can exacerbate pre-existing conditions like asthma and arthritis.
The hypothalamus is the region of the brain that integrates information from different brain regions and is involved in maintaining homeostasis. The hypothalamus communicates with the pituitary gland to cause the release of hormones. These hormones regulate various critical bodily processes including reproductive function. Hormones secreted from the pituitary gland (the follicle-stimulating hormone and luteinizing hormone) regulate the production of testosterone and sperm in the testes of males. The same hormones are also responsible for the regulation of the menstrual cycle in females. Chronic stress affects the function of the hypothalamus and the pituitary and results in the release of a lower amount of these hormones.
Cortisol produced during chronic stress can also disrupt reproductive function at the level of the testes or ovaries. In males, lower testosterone levels due to chronic stress can reduce sex drive. Increased anxiety associated with chronic stress can lead to premature ejaculation and erectile dysfunction. Chronic stress can also disrupt sperm maturation and development resulting in lower sperm motility. Similarly, chronic stress in females can result in absent or irregular menstrual cycles or periods. Prolonged stress can also impact fertility by decreasing the chances of a successful pregnancy.
Long-Term Health Consequences of Stress
Chronic stress can lead to both physical and psychological conditions. Some of the health consequences of chronic stress include increased risk of:
- Cardiovascular conditions like hypertension and atherosclerosis
- Gastrointestinal disorders like inflammatory bowel syndrome
- Sleep problems like insomnia
- Type-2 diabetes
- Headaches and body aches
- Lower sex drive
- Impaired memory and concentration
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