Your body’s reaction to stress -The HPA Axis

You’re sitting in your office happily staring out the window when your computer pings. It’s a reminder you set yourself a month ago. Remember? That really important task your boss set you? No?

Well, it’s due today…

Your heart starts racing, the palms of your hands get sweaty and you feel far too hot. This is the feeling we all know too well as stress. But what actually happens in your body that can turn a simple thought such as “I forgot to do that task” into a heart-pounding physiological reaction?

Stress, Stress, Stress… Well here, we’ve outlined what steps happen to cause the unpleasant sensation of stress in the human body:

1. Evaluating the threat.

   Every day our brains are bombarded with information from the different environments we are in, the people we meet and the thoughts we have. One of the most important jobs our brain has is to filter this information to figure out what is important and what is not. The lady pushing a pram on the other side of the road is not a particularly important signal for our brain but the car hurtling towards us at high speed is. Our brain evaluates the latter as a threat and we jump out of the way to avoid being hit. There are lots of parts of the brain that are involved in this process but the most important is called the amygdala. The amygdala is the Greek word for ‘almond’ because early anatomists thought part of it looked like an almond. When the amygdala detects something which is threatening it sends out alarm bells to the other parts of the brain that it is connected to telling them to be ready to respond.

 

2. Sending out the Army.

   The amygdala sends a message to another part of the brain called the hypothalamus which sends a message further down in the brain to the pituitary gland which then sends a message all the way down to the adrenal glands on top of the kidneys. This is called the Hypothalamic Pituitary Adrenal axis or the HPA axis. When the signal gets to the adrenal glands they release two types of hormones: adrenaline and cortisol. Adrenaline underpins our ‘fight or flight’ response by constricting blood vessels and making the heart pump faster to rush blood to the body and brain. This means our muscles are primed to run away or to stay and fight. It’s probably not the best solution to just run away from your boss when s/he comes to collect your work or, in fact, to fight them, but it would be a useful response if, for example, you came across a tiger in the jungle. Cortisol is the other stress hormone which is released by the adrenal glands in times of stress – this stops the body doing anything which isn’t necessary, such as digesting your lunch, leaving you ready to put all of your resources into dealing with the threat.

3. Returning to normal.

   You tell your boss that you haven’t yet completed the task, s/he understands and gives you another week. Now that the threat is over your stress response system can calm back down. A signal is sent back through all the levels of the brain telling it to switch off the HPA axis. The adrenal glands stop producing cortisol and adrenaline which means heart rate returns to normal, you cool down and your stomach can start digesting your lunch again [1, 2].

 

 

Acute vs Chronic Stress.

The situation above is an example of acute stress. It’s short-lived and quickly resolved. Acute stress can actually be good for us as it sharpens our attention and helps us to perform better, whether that’s running away from a tiger or coming up with some good suggestions in a work meeting [3].

Say, however, you got a reminder every day about a task that you had forgotten to do in work or say your work was piling up so much that you were constantly feeling stressed out all of the time. This is called chronic stress. The HPA axis is a healthy response to short bursts of stress but if we are constantly stressed then our HPA axis is telling the body to increase blood pressure and suppress functions like digestion all of the time. Chronic stress can therefore have damaging effects on health [4]. This is why it’s so important to learn to manage stress.

The good news is that lots of stress management programmes including mindfulness have been found not just to stop you from feeling stressed in your head but also to stop your body’s stress responses from over-activating [5, 6].

So don’t ignore the signals. Managing your stress is not important just for your head but also for your body.

 

Next in the blog – Understanding your Pip Statistics

 

Check out our other blog posts on dealing with stress and see how the Pip can help you kickstart a life in control.

 

1. Smith, S.M. and W.W. Vale, The role of the hypothalamic-pituitary-adrenal axis in neuroendocrine responses to stress. Dialogues in clinical neuroscience, 2006. 8(4): p. 383.
2. Herman, J.P. and W.E. Cullinan, Neurocircuitry of stress: central control of the hypothalamo–pituitary–adrenocortical axis. Trends in neurosciences, 1997. 20(2): p. 78-84.
3. Schilling, T.M., et al., For whom the bell (curve) tolls: Cortisol rapidly affects memory retrieval by an inverted U-shaped dose–response relationship. Psychoneuroendocrinology, 2013. 38(9): p. 1565-1572.
4. Miller, G.E., E. Chen, and E.S. Zhou, If it goes up, must it come down? Chronic stress and the hypothalamic-pituitary-adrenocortical axis in humans. Psychological bulletin, 2007. 133(1): p. 25.
5. Hammerfald, K., et al., Persistent effects of cognitive-behavioral stress management on cortisol responses to acute stress in healthy subjects—a randomized controlled trial. Psychoneuroendocrinology, 2006. 31(3): p. 333-339.
6. Matousek, R.H., P.L. Dobkin, and J. Pruessner, Cortisol as a marker for improvement in mindfulness-based stress reduction. Complementary therapies in clinical practice, 2010. 16(1): p. 13-19.