How emotions affect the meridian system
In acupuncture theory there are sayings about the damaging effects of emotions:
Too much anger injures the Liver
Too much fear injures the Kidneys
Too much sadness injures the Lungs
Too much thinking/worrying injures the Spleen
Too much joy/excitement injures the Heart
Too much emotion injures the Heart
Keep in mind that in the context of acupuncture and Traditional Chinese Medicine the names of the organs when capitalized are not the same as the organs we know from western anatomy. Chinese "Kidneys" e.g. is the adrenals and endocrine system, "Bladder" is the kidneys and urinal system, "Spleen" is the energy system located throughout the body, "Liver" is partly the liver but also something throughout the body, "Lungs" is not only lungs but also skin.
These injuries also have an effect in the other direction: an injured Liver causes anger and injured Kidneys cause fear, etc.