Physiology of Stress

The Physiological Model of Stress: Definition

We often think of stress as something that weighs on us mentally. When we are stressed, our minds are preoccupied with the situation or circumstances causing us stress. These stressors might make us anxious or even depressed. This is grouped as a psychological stress model because it involves how we cognitively react to stress.

However, we experience and process stress in different ways. We know how we psychologically process stress, but what about the physiological model of stress?

Stressful events might affect us psychologically and leave us more prone to depression or anxiety or cause our general optimism to take a hit. Below, let's explore the physiology of stress.

The Physiological Symptoms of Stress

Stress can show up comprehensively across the body, affecting virtually all the body's systems. You might notice shortness of breath or a racing pulse when you become stressed. This is stress acting upon your cardiovascular system.

Stress also affects the gastrointestinal system by causing symptoms such as heartburn or indigestion.

Stress can deregulate our nervous system, affect our sleep cycle, and cause us to feel fatigued or lose or gain weight. Chronic stress has even been known to affect the menstrual cycle and women's ability to conceive.

The Physiological Effects of Stress

Another example of the body's response to stress is altered PH levels. The physiology of stress is when the homeostatic condition of the body changes as a result of encountering stressors. Researchers have identified several parts of the body that are activated when stressed, which are responsible for the physiological changes that occur.

The stress response is considered innate in animals (including humans). If the body is exposed to stress for too long, then the physiological effects of stress can cause long-term damage.

When stressed, many changes occur in the body; the General Adaptation Syndrome (GAS) describes the stages of stress that we experience and how these affect the physiology of our body.

Physiology of Stress: The General Adaptation Syndrome (GAS)

The GAS model was proposed by Selye (1936) to describe what happens to the body when we experience stressors and how the body adapts to stressful situations.

The model states that there are three stages that we experience when we encounter a stressor.

Fig. 2 - Doctor and patient in the emergency room.

The Physiological Impact of Stress

Prolonged stress can leave a lasting impact on the body. It can affect our cardiovascular system and the hormones in our body.

The hormones that are released when we are stressed are adrenaline and cortisol. These hormones are released to stop the adverse effects of stress damaging our bodies.

Adrenaline is released when we are stressed; this hormone affects the sympathetic nervous system and triggers the fight-and-flight response. An increase in adrenaline leads to an increased heart rate, which prepares the by for either:

1. Fight: an increase in energy leads to heightened awareness of your senses so that you are best equipped to fight.
2. Or Flight: an increase in energy so that you can run away.

Cortisol is a hormone that helps regulate blood sugar levels, metabolism and inflammation. Cortisol is also released when we encounter stressors. The hormone ‘turns off’ systems that are not needed in the body. The body is then better prepared to deal with stressors and can stop cells and hormones involved in inflammatory responses from being released.

If we experience high cortisol levels too frequently, it can lead to health issues, such as immunosuppression. Chronic stress causes cells to become resistant to cortisol. Cortisol becomes less effective at stopping cells/hormones from causing inflammatory responses, compromising the functioning of the immune system.

Physiological Causes of Stress

Two different pathways are activated when we experience stressful situations: the Hypothalamic Pituitary Adrenal (HPA) system and the Sympathomedullary Pathway (SAM).

The purpose of the HPA system is to try and maintain homeostasis when we experience stress. The body needs to stay in optimal conditions (like a specific temperature or pH to work properly); this is homeostasis.

When we encounter stressful situations, the hypothalamus is activated, which activates the pituitary gland. The pituitary gland releases a hormone, ACTH (adrenocorticotropic hormone), which is transported to the adrenal glands, the structure responsible for the production of cortisol.

Cortisol turns off the systems, such as inflammatory reactions caused by the activation of the SAM pathway.

During stressful situations, the hypothalamus also activates the adrenal medulla, which is part of the Autonomic Nervous System. The adrenal medulla causes the release of adrenaline that is responsible for the 'fight-or-flight' mode that we enter when we are stressed.

Adrenaline (a hormone made in the adrenal medulla) and noradrenaline (a neurotransmitter made in the sympathetic nervous system) can act as hormones and neurotransmitters. Both help the body prepare for fight-or-flight.