Part 1 – Introduction Into The Biology Of Stress
Is Stress A Headache?
- Yes, but it produces a lot of another physical annoyances (pain, heart beat, insomnia).
- But it is also more than a headache.
- Chronic and severe stress can cause a number of conditions.
- Affects mental and physical health – PTSD, heart disease, arthritis, asthma, and more.
- Research study on monkeys by Uno andSapolsky
- Stressed vs normal monkeys – hypocampus was very physical different.
- Abnormal response – no one is ever that stressed, but impressive result
Consequences of Stress
- Stress related illnesses in US cost us about 100 billion dollars annually.
- Our response to stressors is what makes us sick – the stressors don’t make us sick.
- Every vertebrate has the same response to stress.
- Stress is a label, but it doesn’t describe what is actually happening physically and mentally.
A stressor is a perceived threat to homeostasis – a stimulus. The stress response is an attempt to restore homeostasis. The stress response is the release of stress hormones.
Homeostasis is a property of living organisms to regulate their internal environment in order to maintain stability. Blood pH is an example. If the pH changes from “normal” levels, the body adjusts to return it to normal through a physiological reflex.
A stressor is perceived by the brain, it is processed, and triggers the stress response (fight or flight). Behavior response helps us survive threat.
Stress Response is a physiological response known as HPA axis. The HPA axis is when the hypothalamus releases CRH, the Pituitary gland then releases the ACTH (a neuroendocrine cascade of chemical releases and reactions), the then the Adrenal cortex releases cortisol (corticosterone). This cascade of reactions supplies the body with the necessary tools to evade a perceived threat.
There is also a daily rhythm of cortisol release. Levels peak just before onset of activity (for example, just before waking up).
Stress can be related to reproduction. It can be a threat to one’s ability to reproduce because threats can affect long term success. For example, taking an exam is stressful because can determine your success and ability to reproduce with your desired mate in the long run.
Role of Cortisol
Lion vs. Zebra Chase: Prey and predator both have a stress response during hunt. Cortisol redirects response (energy) towards dealing with the threat.
- Increase in glucose in the blood stream which generates energy to escape/move (lion needs energy to catch zebra, zebra needs to move to escape)
- Increases glucose in the body.
- Increases sympathetic system.
- Decreases parasympathetic system response to turn off unnecessary functions for immediate survival.
- Stress related behaviors increase to escape the threat.
- Alertness increases.
- Once the threat is gone, negative feedback of the HPA axis to turn off stress response.
Part 2 – Importance Of Contexts When Studying Stress
Context matters when determining stressors in an environment. One study by Romero, Reed, and Wingfield in 2000 discovered that tropical birds were more affected by weather changes than arctic birds. Bad weather did not produce a stress response in arctic birds.
Predictability is important in stress. One species of birds stressed about weather changes that were unpredictable. The other species of birds unpredictable weather was predictable and did not stress them out.
Some highly stressful events are predictable (like one’s parents becoming elderly), so there must be other things that contribute. Controllability is important, even when things are predictable.
Example: In a study where rats were put in a wire cage and shocked. The rats that had the ability to control the shock which meant evading the shock were significantly less stressed than rats who had no control. The stressor was the same, but the stress responses were different.
- Ability to escape it with control reduced stress.
- Those that could not control the shock had compromised immune systems.
“CORT is not always anti-reproductive. Neuroendocrine context is important.” Miles Orchinik
Most vertebrates are highly resilient with stress.
Stress as a child can create “abnormal” responses to stress in adulthood. The prefrontal cortex doesn’t act “normally” in adulthood.
Nurture vs. Nature: One’s stress response depends on the environment one grew up in. Birth mother does not matter as much as the nurturing environment one grew up in as a young child. The environment in which they are raised influences their physiological response to stress as adults. (Kim, P. et al., 2013, PNAS)
Is stress a killer?
- Stress increases mortality but only among those who perceived that stress affected their health.
- If they didn’t think it affected them, they did not die at any different rate.
(Keller, A. et al., 2012, Health Psychology)
Anti-Stress Hormone – Oxytocin
The gaze of a dog increases oxytocin levels in dog and the human – increases the bond. (Nagasawa, M. et al., 2015, Science)
Take-Home Concepts To Consider
- Stress is critical in survival and reproduction.
- Stressors produce context specific effects. Context is incredibly important when analyzing the stress.