This is one of the most important aspects of Traditional Chinese Medicine.  Indeed, central to this is the concept of Qi (energy) as a matter-energy that gives rise to physical or mental and emotional phenomena at the same time.  Thus, body, mind & emotions are an integrated whole with no beginning or end, in which the internal organs are the major sphere of influence.
 
This is one of the differences between Chinese & Western Medicine.  While Western Medicine also recognizes the interaction between body & emotions, it does so in a completely different way.  In Western Medicine, the brain is at the top of the body-mind pyramid.  The emotions affect the limbic system within the brain, nerve impulses travel down the hypothalamus, through to the sympathetic & parasympathetic nerve centers, finally reaching the internal organs.  Thus a nerve impulse, triggered off by an emotional upset, is transmitted to an organ.
 
We must, in Chinese Medicine, put the role of emotions in a proper perspective.  First of all, emotions are a natural part of human existence and no human being ever escapes being sad, angry, worried... and all the thousand more emotions we all experience at times.  Emotions only become causes of disease when they are particularly intense & most of all, when they are prolonged over a long period of time, especially when they are not expressed or acknowledged.  Everyone is angry at times, but if someone harbors anger towards another person or a situation for months or years, this emotion becomes a cause of disease.

Secondly, Chinese Medicine is only concerned with the emotions when these are either the cause of disease, or when they themselves are the presenting symptoms.  In other words, Chinese Medicine neither ignores emotions as causes of disease, nor places too much emphasis on them to the exclusion of other causes.
 
Since body & mind form an integrated & inseparable unit, a big web, emotions can not only cause a disharmony, but they can also be caused by it.  For example, a state of fear & anxiety over a long period of time may cause the Kidneys to become deficient; on the other hand, if the Kidneys become deficient through having too many children to close to together, long exhaustive illnesses, too much work for too long without much rest, a too intense sexual life, etc, all of these causative factors may be at the root of a state of anxiety, insomnia, insecurity or fear.
 
There are seven emotions that are usually considered in Chinese Medicine, but this MUST NOT be interpreted too restrictively.  These seven emotions are broad headings under which many other emotions can be included.  Each emotions has a particular effect on Qi and affects a specific target organ.

 
 
Most emotions can, over a prolonged period of time, give rise to what we call Internal Fire because emotions can cause stagnation of Qi & when Qi is compressed for long periods of time it heats and can do so up to creating an internal Fire, just as the temperature of a gas increases when it's pressure is increased.  Signs of internal heat or internal fire will show as constipation, bitter taste, upset stomach, dark urines, cancer sores, etc and the tongue will always be more red than usual.