The Role of the Hypothalamus in Stress Responses

In our daily life, we encounter many stressful situations, be it environmental, such as work deadlines, family arguments or psychological problems, such as worrying about exams, losing a job. An event of stress leads to physical, behavioural, and psychological reactions by the human body. This article dives into the details of the stress response system of the human body.

What is Stress?

Stress occurs when an individual does not have enough resources to cope with the current demands of life. Common responses of the body to a stressful event are heart pounding, sweating, tightening of muscles, and fast breathing. When individuals are caught off guard or feel threatened, a survival mechanism of the body that has evolved over time is known as the “fight-or-flight-or-freeze” response. This is a combination reaction of stress (Harvard Health, 2024).

Response to Stress

Fight – Flight response is a classic sympathetic neurobiological reaction. This is in response to a threat or danger. The first line physiological mechanism is the sympathetic nervous system. The cerebral cortex and brain stem regulate Hypothalamic control of neuroendocrine and autonomic outflow from the limbic system, initiating the fight or flight response (Dieppe et al., n.d.).

The amygdala is the central hub for detecting and emotionally processing the threat. The sensory input of threatening stimuli is received by the amygdala from the thalamus. The information is further passed to the hypothalamus, producing responses in the form of fight, flight or freezing. The freezing response is through the ventrolateral periaqueductal grey and arousal or risk assessment in the basal forebrain (Dieppe et al., n.d.).

Behavioral Changes

Behaviour changes include heightened alertness and arousal. Key regions input in initiating the Fight-or-Flight response are the limbic forebrain regions, cerebral cortex, and brain stem. The central and peripheral responses integrate to coordinate the physiological and behavioural changes (Dieppe et al., n.d.).

How does the Brain Work?

When a stressful situation is experienced by an individual, the sensory organs take in the information and send it to the amygdala. It is an area of the brain that contributes to emotional processing. The amygdala instantly sends distress signals to the hypothalamus (Dieppe et al., n.d.). It works as a command centre of the brain, wherein it communicates to the rest of the body through the autonomic nervous system that there is a stressful situation. The autonomic nervous system is responsible for controlling involuntary body functions such as breathing, blood pressure, heartbeat, etc (Harvard Health, 2024).

Components of the Autonomic Nervous System

There are two components of the autonomic nervous system. One is the Sympathetic nervous system that triggers the fight or flight response, providing a burst of energy so that the body can adequately respond. Another is the parasympathetic nervous system, which promotes the rest and digest response, calming the body after the danger passes. The Sympathetic Nervous System is activated by the hypothalamus through the autonomic nerves to the adrenal glands. The signal pumps epinephrine or adrenaline into the bloodstream, bringing a number of physiological changes in the body (Fight, Flight, or Freeze, n.d., Harvard Health, 2024).

The Role of the HPA Axis in Stress Response

As epinephrine subsides, the hypothalamus activates the Hypothalamic Pituitary Adrenal (HPA) Axis, the second component of the stress response system. It consists of the hypothalamus, the pituitary gland and the adrenal glands. Corticotropin-releasing hormone (CRH) is released if the brain continues to perceive the threat. This, in turn, triggers the release of adrenocorticotropic hormone (ACTH), prompting them to release cortisol. The body stays in high alert till the threat passes. The cortisol level falls, and the parasympathetic nervous system begins to work (Dieppe et al., n.d.).

Physiological Changes During Stress

These physiological changes include a faster heartbeat. Higher pulse rate, rapid breathing, etc. The body intakes extra oxygen as the breath becomes more alerting the brain. The sensory organs, such as hearing, sight, etc, become sharper. Simultaneously, epinephrine triggers the release of temporarily stored glucose (blood sugar) and fats to supply energy to all parts of the body (Fight, Flight, or Freeze, n.d.).

Speed and Efficiency of the Brain’s Response

These processes described above happen so quickly that people aren’t aware of this. The efficiency is so strong that before the brain’s visual centre processes the event fully, the amygdala and hypothalamus start working (Harvard Health, 2024).

Long-Term Impact of Stress

Research has found that long-term chronic stress can contribute to high blood pressure, obesity, artery-clogging deposits, anxiety, depression, and addiction (Harvard Health, 2024). Acute and Chronic stress lead to neuroplastic adaptations that are associated with reduced inhibitory control, impaired executive function, and increased emotional reactivity. Chronic stress is highly associated with dysregulation of the sympathetic nervous system and HPA axis.

Also, it results in persistent hyperarousal, altered heart rate variability, and increased risk for certain neuropsychiatric conditions such as post-traumatic stress disorder, anxiety disorder, depression, etc (Dieppe et al., n.d.). The blood vessels and arteries have the risk of being damaged if persistent epinephrine surges, increasing blood pressure, raising the chances of heart attacks or strokes (Harvard Health, 2024).

Countering the Stress Response

The research studies over the years have found techniques that help with stress responses. These are associated following:

Relaxation Techniques: these include breathing techniques (box breathing, count breathing), focusing on soothing words (peace, calm), and visualisation of tranquil scenes, etc (Fight, Flight, or Freeze, n.d.). A research study was conducted by the General Hospital in Massachusetts on 122 patients with hypertension aged 55 and older. Half of them were assigned relaxation response training, and the other half received information on blood pressure. In results, it was observed that 34 people who practised relaxation techniques (for 8 weeks) had a reduction in systolic blood pressure of more than 5mm Hg (Harvard Health, 2024).
Physical Activity: Exercises such as brisk walking help in deep breathing and relieve muscle tension. Similarly, yoga, tai chi, and qi gong, combined with deep breathing, induce calmness (Harvard Health, 2024).
Social Support: Friends, co-workers, spouse, companions and acquaintances provide a social network that increases longevity. This social net gives emotional support directly or indirectly during crisis and chronic stress (Harvard Health, 2024).
Stress Management: The negative cycle of stress can be dismantled by building resiliency, thus reducing stress and enhancing well-being. Identifying stress warning signs and learning to manage stressful situations better (Harvard Health, 2024).

The Role of the Hypothalamus in Stress Responses: Fight, Flight, or Freeze