Tridosha theory is the foundation of the Indian System of medicine, Ayurveda. To explain the function-correlative, substantive and reproductive of the living matter, the ancient scholars of Ayurveda postulated the concept of Tridosha-the theory of the three somatic humors.The three humors are known as Vata, Pitha and Kapha. Since they are capable of vitiating the dathus and malas (body parts and excreta), they are also known as the doshas. But in a state of equilibrium they maintain and control of the physiological functions and biochemical processes of the body.
The definition of the word Vata clearly explains that this factor or humor is capable of conducting both motor and sensory functions. The physical characteristics, the location and the general functions of Vata have been described.The knowledge that Vata is located in the siras (head) and is responsible for the motor and sensory functions, leads to the conclusion that the important seat of the Vata is the nervous system and that the phenomenon of Vata is the phenomenon of nerve impulse.
The physical characteristics of Vata are quite similar to those of the nervous system. The general functions of the Vata are the following.
1.    Functions related to emotions.
2.    Motor functions.
3.    Sensory functions.
4.    Synthesis of the motor and sensory functions.
5.    Biochemical functions.
6.    Division and differentiation of the cells.
The definition of the word Pitha indicates that, it is responsible for the Paka in the body. The Paka indicates all conversions, transformations and mutations in the body. The functions of the Pitha are stated to be the sanghatabheda dahana, tapana, parinama and Paravritti, etc. On the basis of the knowledge presently available, the substances which perform these functions are the various digestive enzymes, vitamins, hormones, etc.In addition, Pitha is also responsible for some mental functions like intelligence, memory, etc. Pitha is responsible for the major metabolic activities in the body.
The definition of the word Kapha indicates that the major constituent of it is water. A striking similarity exists between the physical qualities of Kapha and those of protoplasm.The functions ascribed to Kapha are the same as those of  cell protoplasm. The locations and functions of Kapha bear a resemblance to some of the special systems of the extracellular fluid, in view of the Ambukarma of Kapha.Tridosha of Ayurveda--vata, pitta, and kapha—consist of systems which regulates controlling the input/ output (moment) in case of Vata, turnover (conversion) in case of Pitha, and storage in case of kapha.
This is the physiological basis around which practical Ayurveda revolves. The Tridosha theory is essentially developed as a tool to measure the pathogenesis and assess the need of healthcare interventions in any given condition.