Dhatu is something that holds or sustains (धारण करना), similar to anabolism (Building up process).
Dhatu is a very important factor as it holds the life force and controls or steers the Dosha. Dhatu is like the hand that holds the steering wheel of Dosha, without which the wheel may throw the vehicle off track and lead to an accident. Imagine a pot which can contain X litres of liquid. Similarly every “body” has an innate and natural capacity to hold a definite amount of Kinetic energy, heat and inertia, in a balanced state. This capacity is governed by the Dhatu system of the body. Stronger the Dhatu system, more will be the total capacity. Stamina is the end result of the Dhatu.
Prakruti also can be defined by the Dhatu capacity. Rasa(lymph) belongs to Kapha, Rakta(blood) to Pitta, Asthi(bones) to Vata. Person with stronger Rakta Dhatu will have higher capacity to hold Pitta Dosha.
If we consider an object, the energy is naturally balanced in it. If it is stable, the energy is in inertia; when falling energy is converted to kinetic energy and when hitting the ground, some heat is also generated. Similar energy conversion is constantly happening in the body to achieve stability. The human body creates and maintains a special internal condition, which helps it survive; and the energy changes are far more complex as compared to a dead object. Stronger the Dhatu system and faster the anabolic processes in a body, lesser are the chances of getting diseases. The body of a child is like this. So a robust Dhatu system can easily prevent damages during the seasonal changes.
7 Dhatu are basic milestones in anabolic route:
RASA – Ingredients that are absorbed by the body after digestion. It is the end product absorbed in the intestines.
RAKTA – Blood
MAMSA – Muscles
MEDA – Fat
MAJJA – Marrow
ASTHI – Bone
SHUKRA – Semen
Dhatu are formed one after the other, means Rakta (blood) will be formed only after Ras (chyme or digested food juice) and not before, directly from the absorbed food. Also the better part of Rasa gets converted to Rakta by the Dhutvagni (Agni is taken as the transformational process or chemical reaction that converts the matter from one form to the other) and same happens with the other Dhatu subsequently. The lesser part gets converted to Mala of the respective Dhatu. It is like the burning of the wood, the better part gets converted to heat and light and the lesser part gets converted to ash.
Shukra is the most important Dhatu in the body. It is said that Shukra finally gets converted into “Ooja”, the life force.