The term Agni is best represented by biological fire. Agni is vital at physiological and pathological levels. Just as we take food stuffs to feed ourselves for nutrition, the so called digestive fire also require constant feeding so as to carry out various biochemical pathways going on in our body.
Majority of the diseases are outcome of malfunctioning of the Agni which rightly has been called as central to health. Agni plays not only plays vital role in absorption of macro as well as micronutrients, but is destructive to pathogens also. The food that in not properly digested is referred as "Ama" in Ayurveda and it nothing but a toxin or pathogen responsible for array of diseases.
Proper functioning of digestive fire is evident from normal tone of the digestive-system circulatory-system, strong immunity or resistance against diseases, proper tissue growth, and above all the complexion. This description better deals with physiological significance of Agni.
If digestive fire is not functioning properly, one has poor digestion, languid blood-circulation, poor complexion, low energy levels, flatulence and poor immunity against diseases. Thus promoting proper functioning of the digestive fire is treating the root cause of the diseases, according to Ayurvedic principles.
In Ayurveda, the theory of Agni or biological fire, is of prime importance. Agni is among the critical factors in determining optimal health and internal haemostasis. On the contrary, Ama is a toxin or pathogen, response for aetiology of all diseases. Major culprit behind Ama production is impairment of Agni, which in turn, destroys Agni. Thus a vicious cycle of impaired Agni and the production of Ama is established. Understanding basic relationship between Ama and Agni is of prime importance in treating a diseases. Maintaining good appetite, use of digestive stimulates and ensuring regular bowel movements are of prime importance in enkindling the digestive fire and preventing the production of root cause of all diseases, Ama.
Normal functioning of digestive fire is mandatory for the proper and compelete digestion of food. Due to low digestive fire the food is not properly digested and Ama (toxic products) are synthesised. Therefore its absorption of Ama becomes sluggish and it retained in the intestine for a longer time. Due to retention, ama undergoes fermentation or sometimes, putrefaction. This toxic product remains unabsorbed in the intestine owing to incomplete digestion and results in diseases like Ama-vata.
Dhatu-agnimandya plays a stellar role in the process of formation of tissues from the nutrient substances (of the particular dhatu). When there is Dhatu-agnimandya the synthesis of that tissue becomes incomplete and ama is formed. Such tissues are called Sama tissues. This type of pathology is seen in various diseases.
Agni is the responsible for transformation of food stuffs in body tissues. In the first stage, Agni produces nutrients, which are converted to tissues. In the second phase of digestion, the action of tissue fire takes place on nutrients of food stuffs, and different tissues are synthesised.
Every biological humour has qualities, which are antagonistic to the qualities of other. The hot quality of Pitta is antagonistic to the cold quality of Kapha and Vata. When two or three humour becomes severely vitiated and combined, they produce interaction between them. In such conditions of antagonism, interaction of opposite qualities results in production of Ama.