The planets can sometimes have a similar meaning to the signs in that if a planet is receiving difficult aspects, than it affect the sign it rules.  But, generally, the planets refer to the action of the body and its reaction to disease.  One would consider the signs as the anatomical correspondence and the planets as the physiology.  In order to understand this, one must first understand how each planets reacts or acts to indicate a possible disease state in the body.  The descriptions that follow are descriptive of a planet involved in some way in a hard aspect or in combination with another planet.

Afflictions to the Sun can result in inflammation, infection, fever, and energy problems.  Sometimes a difficulty with the Sun can indicate a heart problem
in that the Sun is the ruler of Leo which rules the heart muscle.  However, this would need to be confirmed by other planetary indications.
 
Affliction involving the Moon can be descriptive of emotional disorders, water retention, allergic reactions, mucous formation, altered body rhythm, acute ailments, or  female disorders.  Affliction involving Mercury can describe mental or nervous disorders, respiratory disorders, and possibly speech disorders. It can sometimes indicate hormonal problems.

Afflictions involving Venus can indicate an imbalance of bodily energies, benign growths, a blood sugar imbalance, problems with the venous circulation, and a lack of tone.

Afflictions to Mars can result in inflammation and infection, fever, blood ailments, wounds, acidosis, burns, surgery, sudden illness, and muscular disorders.