Dhatus are structural blocks of the body. They constitute the body -termed as S’areera. The most important difference between the Doshas and the Dhatus is that the latter perform functions under the influence of the Doshas. 

The word Dhatu means ‘support’, in Sanskrit. Tissues therefore form the infrastructure of the body. There are Seven types of such structural elements that, constitute human body. 

Rasa :- It represents the primary constitution of human body. Water is a major constituent of human body. Such water is present in human body, both as extra cellular and intracellular fluid content. Rasa dhatu-the first of seven structural elements refers to both extra cellular and intracellular portions of fluid in the body.

Rakta :- The word Rakta refers to Blood. Thus, Rakta dhatu represents the blood, which includes its cellular components. Blood is perceived as a special type of tissue, in modern concepts of physiology also. 

Mamsa :- The muscular tissue, which constitutes many internal organs as well as the muscles, is referred to as Mamsa.

Medas :- Medo-dhatu is referred to as adipose tissue. Commonly, adipose tissue comprises of all deposits of fat-distributed in the body. 

Asthi :- All the bones in human body are composed of a tissue termed as osseous tissue. All such tissue is termed as Asthi dhatu in Ayurveda. Asthi dhatu also include all cartilaginous structure in the body. 

Majja :- Majja is bone marrow. A special type tissue called myeloid tissue forms bone marrow. 

Sukra :- Sukra represents the reproductive elements. This includes the sperm in males and ovum in females. Apart from these elements, Sukra also refers to cellular reproductive elements.

TISSUE NUTRITION IN AYURVEDA

The mechanism involved in the maintenance of nutrition to these 7 structural elements is explained in a concept; known as " Dhatuparinama Vada".

As per this concept, the ingested food is digested in digestive tract and nutrient and waste parts are segregated. This kind of digestion is carried out primarily, by Pachaka Pitta-which is the digestive moiety of Pitta. 

Samana Vata and Kledaka Kapha, which are the functional moieties of Vata and Kapha respectively, located in digestive system, support Pachaka Pitta in this process. In view of its fire like role, Pachaka Pitta is referred to as "Pachakagni".

This process can be explained very simply, with an analogy of "Cooking". We need the help of air, fire and water to cook food properly, in our day today practice. In our body, functions of air, fire and water are played by Samana Vata, Pachaka Pitta and Kledaka Kapha respectively. A right degree of cooking is possible when the air, fire and water are just, at optimal level. 

After digestion, the nutrients and wastes from ingested food are segregated. The digested food, termed as " Ahar Ras" is a blend nutrients needed for all 7 dhatus.

Nutritional demands of different dhatus are variable and each dhatu derives its selective nutrients, as this "Ahar Ras" is circulated through out the body through circulatng channels. The selective nutrient, picked-up by each Dhatu, undergoes further metabolism in respective tissues.

Such metabolism, within a Dhatu is carried out with the help of specific moieties of Pitta located in respective dhatus. The Pitta element, working within a particular dhatu, is called as Dhatwagni.

During this process, each Dhatu produces some kind of metabolic waste again, from its selective nutrients. Such wastes produced by a Dhatu are called Dhatumala. If not eliminated from time to time these wastes from tissues become toxic. Therefore, Ayurveda recommends periodical "cleansing" of body