Man is a miniature world and a specimen of the greater world as has been said by Amirul Momineen Imam Ali (a.s.):
“Do you think that you are merely a tiny body?
A great universe is hidden in you. The bones in your body are like mountains of the earth and the flesh is like dust.
The big and small veins are similar to rivulets.
Man’s head, which is the centre of his strength and intelligence, is like a sky above the body containing stars etc., which throw light on earth.
The vapours rising from stomach and reaching brain and after cooling drop from eyes and brain are like those vapours, which rise from the earth and reach the cold strata of upper space and then drop in the form of rain.
Moreover, the powers of brain reach the entire body through the back brain nerves just as the starlight affects the earth.
Just as there are kings and commanders in the world on earth so also there are some servants and rulers in the body too and their king is the faculty of speech, which is also called Qalb (heart) from the viewpoint that first its relation is with the animal spirit and then it is nourished by the heart.
Just, as the world’s habitation is in the north so also the heart, which is the cause of the habitation of the body, is in the north.
Just as the kings have their ministers who distribute sustenance to the ruled so also whatever is cooked in the kitchen of liver is being distributed in the entire body.
Just as some earthly wastes are disposed through rivers such arrangement is also in the human physique.
In short, a detailed discussion of this topic demands much space for which this is not an appropriate place.