According to Ayurvedic system of medicine, rasa represents the first dhatu. Rasa is the major and primary constituent of the human body. Rasa represents the fluids (extra cellular and intracellular parts) of the human body and it mainly concerned with nourishment and strengthening the blood. Once the process of digestion of the food is complete, it gets converted into a liquid (chyle) which undergoes transformed into blood tissue.
When the rasa or plasma undergoes refining, then it is known as rakta dhatu (blood tissue). Rakta dhatu is mainly concerned with nourishment of the body by carryng macro and micro-nutrients to the body-cells and tissues of the human body through the circulatory system or the blood vessels. Rakta dhatu is preserver of life and plays major role in gaseous exchange.
Mamsa represents the muscle that enters into the constituents of the internal organs of the human body. Mamsa dhatu is derived from the rakta dhatu and constitutes the cover of structure and bone of the human-body.