Felt the effects of stress recently? Who hasn’t? Psychological stress can heavily impact our mood, behavior, and social interactions with others, but it can just as easily affect us internally, in ways we never fully realize.

What we think of as feeling stressed is really a series of internal events that shift your body into ‘survival mode’ in response to external psychological stressors. You may simply be scrambling to finish a presentation, not dealing with the death of a loved one or fighting off a bear attack, but your body’s response is more or less the same.

It’s also a lot more complicated than you realize: Your response to stress taps into four different physiological systems. It starts with your adrenal glands, which are part of your endocrine system. Typically, acutely stressful events cause increased production of stress hormones such as cortisol and the catecholamines.

Dealing with stress requires physical energy, so these hormones work together to make energy readily available for you to burn through by breaking down body fat and mobilizing our stores of glucose into the bloodstream. This immediate energy is then ready to be used as the body needs it, whether that is for the fight-or-flight response or for adaptation to long-term stress. Some theories suggest this increased need for energy could be responsible for overeating as a response to stress in some people and weight loss in others.

At the same time, the adrenal hormones activate your sympathetic nervous system, which in turn triggers immediate responses in your cardiovascular system: Blood vessels clamp down and send blood where it is needed most – your vital organs. If you’ve ever felt like your heart was racing in a particularly stressful situation, this is why.

Last, but certainly not least, stress activates your immune system by making immune cells more readily available in your bloodstream, so they can be ready to help your body fight infection or injury. While infection and injury generally aren’t the primary stressors in our lives any more – over time, our bodies have evolved to recognize other events as stressful — your immune response even to psychological stress remains the same.

In a passing stressful experience, what stress does to the body may not greatly impact our lives; we may feel tired, we may feel like our heart is racing, but generally these feelings will be temporary, stopping soon after the stress ends. This is why there is some truth to the common notion of getting sick after a stressful event passes: Your immune system, which was once on the up-and-up, drops its defenses when the stress subsides, so your body is then — at least theoretically — at more risk of catching minor illnesses.

However, continuous exposure to stress can lead to chronic changes that are detrimental to overall health. Over time, our cardiovascular systems take a hit. Chronic stress can lead to damaged blood vessels that can then lead to an increased risk of heart attack and stroke. How chronic stress facilitates this damage is still being somewhat of a mystery; some theories suggest that chronic stress — and thus, chronic immune system activation — can cause immune cells to release pro-inflammatory markers, which damage blood vessels over time.

Interestingly, the opposite can prove true, too, in the long term. Ongoing stress can actually cause immune suppression over time and make us more prone to infections, poor wound healing, and slower recovery from illness. This is because the signals that mediate our immune system’s stress response can actually become dysfunctional when ‘on’ all the time.

Other functions can become dysfunctional, too. Long-term stress causes long-term mobilization of energy, partly in the form of increased blood glucose, as mentioned earlier. This chronic exposure to high glucose levels in the blood has been implicated in the development of insulin resistance, which can lead to diabetes.

In other words, stress does more than make us snappy. In the long term — over years, that is — the effects of stress can directly contribute to diabetes, heart disease, immunosuppression, and more. While we cannot ever avoid stress entirely, particularly anyone with stress due to underlying health conditions, we can at least try to avoid sweating the small stuff. Take some deep breaths, and try not to get too worked up about that upcoming deadline at work — you and your body deserve better than that.