Upadhatus (Sanskrit: उपधातवः) are secondary body tissues in Shariram (शरीरम्). According to Ayurveda, there are few body tissues that perform specific function in the body but they are ranked next to the main 7 Dhatus (धातुs) on the basis of their function and role in the maintenance of life. Such tissues develop from and derive their nutrition from main Dhatus. For every upadhatu there is one parent Dhatu. Description of around 7 such tissues is available in various Ayurveda treatises.
- 1 परिचयः ॥ Introduction
- 2 व्युत्पत्तिः॥ Etymology
- 3 व्याख्या॥ Definition
- 4 विविध धातवानां उपधातवः॥ Upadhatus of Dhatus
- 5 उपधातु उत्पत्तिः॥ Upadhatu formation
- 6 References
परिचयः ॥ Introduction
Doshas, dhatus and malas are considered roots or functional biological units in the body. However, apart from these 3 there are certain other components that are related to these basis units but differ in their function and role in the maintenance of Ayu. Upadhatus are such important physiological units in Sharira which have certain specific function to render. They are derived from Dhatus and resemble Dhatus in terms of structure, function and nature. Updhatus are derived from the first four Dhatus. Updhatus are end product of Dhatu metabolism.
The word, Updhatu has been made by combination of two words i.e Upa- and Dhatu.
- 'Upa" is a prefix attached to the word "Dhatu". Prefix changes the meaning of the word with which it is acting. The literary meaning of "Upa is Towards, near to, by the side of, resemblance, nearness, with the idea of subordination n inferiority.
- Dhatu form the Basic architecture of the body, they are not accomplished to execute the functions of the body without the support of Updhatus.
so, Updhatus are basically the derivatives of the Dhatus and resemble Dhatus in terms of structure, functions and nature.
The commentator Chakrapani has used the term Upadhatu while describing the dhatu level metabolism and its by products. At the same place he has given the reference from Bhoja Samhita, which provides the definition of the term Upadhatu.
सिरास्नायुरजःस्तन्यत्वचो गतिविवर्जिताः। धातुभ्यश्चोपजायन्ते तस्मात्त उपधातवः ॥ (Char. Samh. 15.17 Chakrapani Commentary)
sirāsnāyurajaḥstanyatvaco gativivarjitāḥ। dhātubhyaścopajāyante tasmātta upadhātavaḥ ॥
Meaning: Elements of the body which are derived from Dhatus and which are not further subjected to any transformation are called Upadhatus.
विविध धातवानां उपधातवः॥ Upadhatus of Dhatus
Acharya Charaka has described 7 products of Dhatu metabolism but has not used the term Upadhatu for them. 
रसात् स्तन्यं ततो रक्तमसृजः कण्डराः सिराः। मांसाद्वसा त्वचः षट् च मेदसः स्नायुसम्भवः ॥ (Char. Samh. 15.17)
rasāt stanyaṁ tato raktamasr̥jaḥ kaṇḍarāḥ sirāḥ। māṁsādvasā tvacaḥ ṣaṭ ca medasaḥ snāyusambhavaḥ ॥
Later the commentator Chakrapanidutta has termed them 'Updhatu' and also elaborated the difference between Dhatus and Upadhatus clearly. He calls them Upadhatus since they are not subjected to any further transformation or processing and thus do not generate any other body constituent. 
Acharya Charaka has described Upadhatus of first 4 dhatus as follows,
- रसः Rasa - Stanya, Raja
- रक्तम् Rakta - Kandara, Sira
- मांस Mamsa - Vasa, Twak
- मेद Meda - Snayu, Sandhi (Dalhana)
There is no mention about Upadhatus in Sushruta Samhita clearly. But the upadhatus mentioned by Acharya Charaka have been described in detailed manner in his work.
Stanya refers to the breast milk. Hence it is the upadhatu present only in females and related to reproduction. It derives its nourishment from Rasa dhatu. Performs the function of providing nourishment to the infant.
Rajas or Raja means the menstrual blood. This one is also the female specific upadhatu and appears in a particular reproductive age group in females. Performs the important function of providing seat and nourishment for embryo in initial period.
Commentator Charkrapani has defined Kandara as the 'Sthula Snayu' or 'Sthula Sira'. These are upadhatu of Rakta dhatu and assist in the function of locomotion.
Upadhatus of Rakta dhatu. Sira refers to the vascular structures in the body that perform the function of transport, circulation, transmission of bodily elements. The root term 'Sru' from which the word 'Sira' is derived indicates flow.
Mansa dhatu's upadhatu is 'Vasa'. The term 'Vasa' is coined on the basis of its function of covering the body or wrapping the body, abdomen etc. It refers to the fat that fills up various muscle spaces, covers vital organs and supports or protects other structures like vessels and organs.
Twak is the Samskrit term for Skin. It is the outermost covering layer of the body. It protects the entire structure of Shariram and thus plays important role as the barrier between external and internal environment. It is the upadhatu of Mansa dhatu. It is believed to be composed of 6 layers.
Upadhatu of Meda dhatu. These are the body constituents which bind any 2 body structures at their joint. Such joints are called as Sandhi in Ayurveda. Thus, they perform the function of holding the entire structure together. Classics have described Nine hundred Snayus.
Sandhi refers to joint between any 2 or more structures in the body. Commentator Dalhana of Sushruta Samhita has described Sandhis as Upadhatus of Meda dhatu.
उपधातु उत्पत्तिः॥ Upadhatu formation
Dhatu metabolism is a nourished pool of all the body constituents. Through this pool all elements including Upadhatus derive their nourishment and maintain their equilibrium. The nutrition for all the body constituents is derived from the essence of the food that we eat. This essence is formed after appropriate action of Agni on food and formation of good quality Rasa dhatu from it. This rasa dhatu contains nourishing elements required for growth and development of all the body constituents. Thus, it is called as essence that nourishes body and is in the pure form. On this essence action of agni of all dhatus takes place and selective absorption happens. From the purest form of the absorbed nutrients dhatus and respective upadhatus are formed in progressive order.