As a senior in my final weeks of college, I’m facing a gargantuan amount of stress. Final exams, papers and projects are here, on top of the obligation to graduate and find a job. No pressure.

Despite the fact that I know I’ll find a way to get everything done, my body is still reacting to my stress in a very real way: insomnia, changes in appetite and an increased heart rate. But why does a mental state result in long-lasting physical symptoms?

I’ve discussed ways the body instantly receives information using neurons. The endocrine system, a complex of glands and hormones, is another way of sending messages through the body; however, these are slower and longer lasting. If the messages sent through neurons are text messages, then those sent by hormones are hand-written letters — arguably classier and more meaningful, but slower in transmission.

The endocrine system operates using glands that produce those hormones. You have your pituitary gland that sits in the brain and your adrenal glands that perch atop the kidneys, plus many others, including the better-known pancreas. Each gland monitors the blood and secretes its particular hormones in order to make adjustments throughout the body.

So when we experience stress, known as that “fight or flight” response, there’s an upregulation of a lovely hormone called cortisol. Cortisol is controlled by the hypothalamic pituitary adrenal axis, also known as the HPA axis.

The hypothalamus isn’t actually an endocrine gland but rather a region of the brain that communicates with the pituitary gland and keeps the body in a healthy and balanced state. Remember where the pituitary gland is? Not only is it in the brain, but it’s right below and connected directly to the hypothalamus. The last member of the HPA axis is the adrenal glands, which if you recall are on top of the kidneys.

Whether faced with a menacing grizzly bear or eight finals, the stress “fight or flight” response is triggered and cortisol is upregulated after a chain of responses. Your eyes perceive the threat, and those special neurons carry that message immediately to several regions of the brain that toss that information to the hypothalamus. The hypothalamus “texts” the pituitary gland, which “writes a letter” to the distant adrenal gland that the body needs some cortisol.

The adrenal gland releases the cortisol into the blood, and the blood carries it throughout the body to prepare it for fight or flight. To do either of those, the body prioritizes muscle usage. This means shutting off unnecessary systems like the digestion and immune system, hence changes in appetite and increased illness.

Muscles need energy, so cortisol increases glucose, sugar and inhibits its storage. Muscle cells need oxygen too, so cortisol opens your airways and accelerates breathing. And, in order for your muscles to receive all this glucose and oxygen, cortisol narrows the arteries and another stress hormone, adrenaline, increases your heart rate, altogether pumping your blood much faster.

Woah, where did adrenaline come from? The adrenal gland put the “adrenal” in adrenaline and secreted it at the same time as cortisol.

So now what? Whether faced with a grizzly bear or series of finals, don’t panic. Talk calmly but don’t flee because both can easily outrun you. Keep your backpack on because it can help protect you, and if attacked, play dead.