The flow of nutrients and other materials has to be maintained to see that all the body tissues get adequate amount of nutrients and other essential material. The channels are facilitating this job. These channels are called as Srotas. In general term Srotas comprehends all channels- big and small, perceptible and imperceptible- that compose the internal transport system of the body. There are several synonyms used for the term Srotas viz. Srotamsi, Siras, Dhamanis, Rasayanis,Panthanas etc. These channels acquire the shape and color of the Dhatu that they transport. These channels are big as well as small depending on what they are required to carry. These Srotasas can be cylindrical, minute or microscopic (anu) or dirgha(long). These srotas are the channels that perform the function of transformation, transportation excretion, maintenance, growth etc. Charaka, Sushruta and Vaghabhatta all the three main Samhitas have described these Srotasas in great details. The srotases described are as under:

Vata, Pitta, and Kapha are stated to traverse the entire body and move through different kinds of srotasas

In common language Agni means fire. But in the context of functions of the biological system that which converts all that is ingested to structural and functional constituents and provides for the energy is some thing that is termed as Agni in Ayurveda. The net result of Agni would mean better conversion of ingested things in to body tissues and better generation of energy required for carrying out various activities in the human system. Ayurveda has laid lot of importance on Agni i.e. the digestive power or the transformation force. Our health mainly depends on what we eat. Agni is responsible for the proper digestion of these consumed foods etc. Ayurveda believes that all diseases are primarily because of a weak digestive/transforming power. Agni is basically divided into 13 types with the Jatharagni or the digestive power of the stomach / abdomen as the main Agni. The other seven are Dhatu-Agnis (one of each Dhatu), five Agnis of each of the Panchamahabhootas. These 12 Agni are responsible for the proper nourishment of the body. Along with digestion and transformation of the ingested food, a proper disposal of waste products is also the funciton of these Agnis. A defective Agni leads to the development of Ama or undigested part which when circulates in the body gives rise to various diseases.

A systematic description of principles of Ayurveda is done in all the major Samhitas(Classical Texts) of Ayurveda. Charak Samhita has described Six Padarthas as the factors that determine the complete life and knowledge of Ayurveda. They are the Dravya (matter) and Guna (properties), Karma (function) Samanaya (Similarity), Vishesha (Dissimilarity / individuality), Samavaya (components responsible for continuity). An Ayurvedic physician is expected to have a complete knowledge of all these factors before he starts practicing the Ayurvedic system of medicine.

Ayurveda believes that nothing can happen without a cause. A particular causative factor is responsible for the development of particular effects. This is called as the cause effect relationship in Ayurveda. This is one major principle on which Ayurvedic diagnosis and treatment are based.

The one most extensively used & practically applicable principle of Ayurveda is the Samanaya Vishesha principle. According to this principle similar properties of an external factor are responsible for the development of similar properties and functions in the human body. Conversely dissimilar properties or dislike properties are responsible for development of opposite properties or functions in a human body. For e.g. the consumption of flesh/fat will increase the muscle, fat in our body. This similarity / dissimilarity is divided into three major parts like.

1. Dravya Samanya(Matter similar) e.g. Blood increases blood.
2. Guna Samanya(Property similar) e.g. Milk increases strength.
3. Karma Samanya(Function similar) e.g. exercise give strength.

Similarly the principle of dissimilarity is also applicable and that is of the three same types as mentioned for Samanya.

Ayurveda has also described the means of knowledge or proofs (Pramanas). It accepts four such means of acquiring correct knowledge viz. 1) Pratkyaksha Pramana or direct perception via the senses and mind 2) Anumana Pramana or drawing inferences from circumstantial evidences without making any direct perceptions 3).Yukti Pramana or analogy 4)Shabda Pramana or words spoken by a knowledgeable persons or references from very reliable literature. Ayurveda accepts these as four means of knowledge in arriving at the truth of things.

Ayurveda believes that when a state of disease appears the components which are deranged shall by themselves undergo a phase of regression i.e., there is a tendency of the body to revert back to normalcy and hence the diseases slowly subside completely on their own. A physician has thus only to develop the body's defenses and make them so strong that the anomaly goes away on its own and that it does not return back. Therefore Ayurvedic methods are usually tissue protective. One has assure that the causative factors responsible for the development of disease have been taken away and that the tissues are well protected with adequate defensive strength.