Represents the individual constitution expressed through ascending signal and element (nature).
It is said that a planet in 1 house with its aspects is related to an inherent feature of someone’s physical body.
With such interest, you can find well that the study of medical astrology fits you like a glove. 
Example:
Explaining the Natal aspects, my first astrological teacher said that in a 1 house, Mars will suffer from harshly identified ‘An electric shock for the system’. Can’t do not do W.Old. It was worried to me because I knew someone with a Capricorn ASC., Mangal in intercepted Aquarius 150* Moon in cancer in 6th house, and square Saturn in Taurus.
In mid-life, the person was suffering from an inflammation (Mars) peptic stomach (body cancer area) ulcers.
Late in life, a person suffered a blood (Mars) clot (Saturn) to the cerebral bleeding stroke.
Deep or pre-determined ????
