Rasa dhatu is the first amongst the seven dhatu. ' Rasa' literally means 'one which moves continuously'. Rasa dhatu is the essence of the ingested food, which continuously circulates in the body and provides nourishment. In its course of circulation, it executes the functions of tarpan (nourishing), vardhan (to grow - as in case of a child), dharan (to hold - as in case of youth), yapan (to maintain - as in case of aged person) of the body, by adrushta hetukena karmana (the action that cannot be perceived).
Stanya (breast milk) and artava (menstruation) are upadhatu (secondary tissue) of rasa. They are formed during the action of rasa dhatwagni on rasa dhatu within its srotasa.
During the process of formation of rasa dhatu in rasawaha srotasa, mala roopa kapha (excrement kapha) is also formed. This kapha is diffrent from kapha dosha. The former is formed in rasawaha srotasa, where as later is formed in amashaya (stomach) during digestion.
Rakta is the second dhatu. It is red in colour and its main function is jeevan (to maintain life). Apparently rakta dhatu looks similar to blood. However, unlike blood, rakta dhatu, according to ayurved, plays a greater role in pathology of disease and its treatment.
Kandara (ligaments) and sira (vessels) are the upa-adhatu of rakta dhatu .
Mala roopa pitta (not the pitta dosha) are the mala of rakta dhatu.
Mansa (muscle tissue) is the third dhatu . The main function of mansa is lepana (coating or covering). It also strengthens the body and provides posture. It carries out all the physical activities of the body.
Its upadhatu is Twacha (skin) and vasa (fats).
Kha mala (excretory waste material found in the ear, eye, nose, mouth and genitalia) are the mala (excrements) of mansa dhatu.