The sole purpose of metabolism is to assemble proper ‘Dhatus’ together in synchronization with which they carry out their role as the field of physiological activity. Dhatus which are of seven different types work in coordination with one another.
They are: life sap (rasa), blood (rakta), muscles (mansa), fatty tissue (med), bones (asthi), bone marrow and nervous tissue (majja) and semen and reproductive system (shukra).
It works in such a way that one tissue or dhatu transforms to the next from the nourishment they get from the digestive sysytem.There are seven dhatus in all rasa, rakta, mansa, med, asthi, majja and shukra.So from rasa (life sap) the body develops rakta (blood), from rakta it develops mansa (muscles), from mansa is developed med (fat), from med is developed asthi (bones), from asthi the body develops majja (nervous system) and from majja is generated shukra (semen).
Thus according to ayurveda the seven dhatus are responsible for the immune system. The best thing about Ayurveda is that they follow a very specific method of treatment for diseases related to different dhatus.The growth and survival of the human body depends on these dhatus or the tissues.
These seven dhatus are in turn made of five mahabhutas.When there is a slight disturbance or imbalance in the equilibrium of these dhatus it will result in ailments or diseases of the human body.
The Ayurveda see body as whole compartment and finds the root causes of the disease The imbalance in these dosha or transforming of Dhatus are the real cause of disease, by just make proper adjustment in your diet and lifestyle the dosha and Dhatus can be brought to balance thus making a person healthy or a man can live up to long life.