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How Herbs Work
Herbs acts by its potency. Potency of herbs implies all the qualities of herbs by which they act, via rasa, vipaka, guna, veerya and Prabhava. Rasa and Vipaka indicate the chemical structure of herbs, and guna and veerya indicate the physico-pharmacological properties of herbs. Different herbs have got different arrangements of the five proto-elements in terms of weight, number and configuration in their composition. The specific arrangement of any two of the proto-elements gives rise to a particular taste of a herb. Therefore, the predominant proto-elements in a herb are inferred from it’s taste. The specific taste inherits the specific qualities from it’s predominant proto-elemental constituents. Rasas have got certain local and systemic actions on account of their qualities. After the herbs ingested, it has to be digested by the gastric enzymes (pachakagni) and metabolized by different enzymes and hormones (bhautikagnis and dhatwagnis) in the liver and tissues. During these processes, the herb is broken down and reformed or re-synthesized, and this is what is known as Vipaka. If the elemental composition of the re-synthesize or resultant substance remains the same as that of the original herb, the pharmacological properties will not change (samana pratyayarabdha dravas). But if the composition of the synthesized or resultant substance changes, it’s pharmacological properties will also change. (vichitra pratyayarabdha dravyas). For example, if a herb of madhura rasa changes into Madhura vipaka and, therefore, possesses the qualities of Guru and sheeta, it is a Samana pratyayarabdha Dravya as the proto elemental composition of the herb and it’s qualities have not changed during digestion and metabolism. But if an herb of madhura rasa changes into Katu Vipaka and, thereby, acquires the qualities of Laghu and Ushna, it is a Vichitra Pratyayarabdha Dravya. Such changes may take place at the level of Pachakagni, Bhautikagnis and Dhatwagnis Corresponding to Digestion, intermediary metabolism and Cellular metabolism.
The actions of a herb are intimately related to it’s chemical structure (rasa and vipaka). For an easy understanding, it can be said that what gunas are to rasas, veeryas are to Vipakas’. A herb performs certain local and general actions by it’s Rasa and Guna, and certain specific therapeutic actions by it’s Vipaka and Veerya.
Prabhava is a term, which corresponds to isomerism and isomer ides, Substances similar in composition in terms of weight and number of the proto-elements may differ in some actions if the proto-elemental configuration is different. Says charaka: “where there exists a similarity in taste, potency and post digestive changes and yet a difference in actions is observed, such special difference in action is called the specific action (Prabhava) of the substance.”
“The manifold virtues accruing from wearing precious stones and herbs on the body are also due to specific action, and such a specific action is considered inexplicable.”
“Some substance act in accordance with their tastes, others in accordance with their potency, and yet others in accordance with their qualities or post digestive effects or specific action”.
“When taste and the rest are evenly balanced in their strength, the following is the normal order of their relative influence, Post-digestive effects are stronger and more powerful than the preceding two, while specific action is the most powerful of all” (Charaka).
In order to produce the main desired effect, a herb must be present in appropriate concentration at the site of action. The optimum concentration of a herb depends upon the dose administered and the extent and rate of it’s digestion, absorption, localization or Biotransformation and excretion.
The digestion and absorption of herbs should be understood on the lines of formation and absorption of the Poshaka Doshas in the Gastro-intestinal tract. The whole G.I. tract is functionally devided into three parts according to the sites of the Doshas therein.
- Kapha, having Snigdha, Sheeta and Guru Qualities, is formed in, and absorbed from, amashaya.
- Pitta, having Snigdha, Ushna and Laghu qualities, is formed in, and absorbed from, Grahani.
- Vata, having Ruksha, sheeta and Laghu qualities, is formed in, and absorbed from, Pakwashya
Therefore, the herbs having the Rasa and Vipaka of the above qualities are digested in, and absorbed from, the above places in the gastro intestinal tract. The herbs, which are snigdha (lipid soluble) and Sheeta (non-ionised) are absorbed through the gastric and intestinal mucosa. If the herb molecule is bigger in size (guru) it can not pass through the mucous membrane but is absorbed through the vesicular transport. Here are some details according to text
- Madhura rasa dravyas (Snigdha, Sheeta, guru) are absorbed by way of diffusion across the gastro-intestinal epithelium or by way of the vesicular transport.
- Amla Dravyas are snigdha, Ushna (ionized) and laghu (small molecule) and they can be readily absorbed through the gastro-intestinal mucosa.
- Katu. Tikta, Kashaya dravyas are transformed into Katu Vipaka, which is Ruksha (water soluble) Sheeta (non-ionised) Laghu (small molecule) and such herbs are readily absorbed through the mucosa of the small and large intestines.
There can not be any hard and fast the (rule) about the absorption of herbs from the above mentioned specific places only, as many factors play their part in it, viz, the condition of Agni (ph of the gastric contents), duration of stay of herb in a particular place, and the solubility and concentration of herbs.
The absorption is also affected by the mode of preparation and the mode of administration.
- The water soluble fractions of herbs should, therefore, by administered in the form of kashaya Kalpana
- The fat soluble fractions of herbs should be administered in the form of fatty preparations like Taila or Ghrita.
- The herbs, whose potency can better be preserved in alcohol should be administered in the form of asava and Arista as they are easily and quickly absorbed from the gastric mucosa in the Amla medium.
- Gaseous and volatile herbs can be inhaled and absorbed through the pulmonary epithelium and mucous membrane of the respiratory tract. Use of different kinds of inhalations in Sawasa Roga has been advocated and quick absorption of such herbs bring quick results, notwithstanding their local effect.
- Herbs locally applied in the conjunctive, naso-pharynx, oropharynx, vagina, colon, urethra and urinary bladder are absorbed through the mucous membrane of these organs.
- Herbs are also absorbed through the skin in small, yet effective, quantities, Epidermis behaves like a lipid barrier and, therefore, the lipid solubility of the substance is necessary for absorption through the skin. This is one of the reasons why oily preparations are locally used for injunction in various Vatika disorders. The dermis is freely permeable to many solutes. Systemic absorption of herbs through the skin occur much more readily through the abraded or denuded skin (dermis) This is why in case of bites by poisonous insects or snakes, the skin is denuded and then, medicines are applied locally. It is not necessary for each and every herb to be subjected to digestion.
- The Vyavayi dravyas, whether orally ingested or locally or parent rally administered, are quickly absorbed and metabolized. Obviously, such herbs yield quick results.
Herbs reach their site of action of stimulates or depresses the Doshas, dhuatus or Malas as the case may be. This is regulated by the principles of Similarity and dissimilarity. As a result of the actions of the Bhautikagnis and Dhatwagnis, herbs are metabolized and excreted through urine, stool or sweet. Also the herbs coming in contact with a particular dhatu are bio-transformed and excreted along with the mala of that dhatu. The metabolism of herbs depends upon the Bhautikagnis in the liver and the Dhatwagnis in the cells or tissues.