How does an anxiety disorder cause the adrenal glands to affect the body?

I have an anxiety disorder….it is GAD (generalized anxiety disorder) stemming from panic disorder. If I am constantly worrying that I have a brain tumor (I'm 14) and that I'm going to have a seizure at any given moment, how can my adrenal gland affect my body? People in the medical field or with experience only please….thank you!