In times of stress, activation of the sympathetic nervous system results in the adrenal gland secreting hormones that tend to:

Stressful conditions activated sympathetic nervous system which shows a fight and flight response by preparing adrenal glands to release specific hormones during stress. During fight and flight conditions, adrenal medulla releases certain hormones:

- Epinephrine or adrenaline

-Norepinephrine  

These two hormones releases from adrenal medulla during stressful conditions. They tend to spike up the heart rate and blood sugar level by breaking down more glycogen into glucose. They also increase the heart flow towards brain and muscles.  Norepinephrine also cause vasoconstriction which is the narrowing down of blood vessels results in high blood pressure.

it would lead to upper respiratory infections and pneumonia.