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The constituents of medicinal plants - Pengelly A.

Pengelly A. The constituents of medicinal plants - London, 2001. - 109 p.
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My wife Sunny is a herbal “true believer", and I wish to express my thanks for her constant support and encouragement, without which this book would have been just another idea.
The main purpose of writing this book was to present a relatively simple introduction to the chemical constituents of herbs for students of medical herbalism in Australia. Since the first edition in 1996, this text has been included in the curricuJums of most natural therapy colleges in this country, as well as in New Zealand and at least one U.S. institution. Principles and teachers from several of these colleges have observed the lack of an existing appropriate text on the subject, the only comparable texts being far more comprehensive and costly usually aimed at the post-graduate scientist or pharmacist rather than the undergraduate. Nevertheless the book has also proven popular with graduates and health-care practitioners, many of whom enjoy having a ready reference to the complex area of plant constituents and therapeutic activities associated with them.
The purpose of this second edition is not to present new material, rather to tidy up a number of typographical and spelling errors that slipped through the proof reading in the first edition. In the nine months since first publication, the text has been carefully scrudnized by various experts and authorities in herbalism and plant chemistry, and apart from some minor disagreements no technical errors have been identified. This is important since I anticipate the book will remain a standard reference in this field for many years to come.
In presenting material of the nature of the topic under discussion, there is always a danger of becoming obsessed with the chemical structures themselves, and presenting these as the main rationale for the therapeutic activities of plant medicines. While not underestimating their influence
I believe the constituents are but one explanation of a herb’s activities, not necessarily more or less relevant than
other factors. I am primarily a holistic practitioner but I do not believe we can disregard the increasing information becoming available to us through modern research, even though this research may be based on reductionist principles. It is encumbent on practitioners and teachers of plant medicine to stay abreast of the research, but our interpretation and application of the research should be based on a holistic understanding of the herbs and of disease processes.
Chapter 1
There are two fundamental ways in which herbal medicines may be classified - according to their energetic qualities and their phytochemical constituents. Energetic qualities are highly valued in traditional systems such as Ayurvedic and Traditional Chinese Medicine, but less so in Western medicine. Through application of pharmacognosy
- involving study of herbal medicines from all perspectives
- it is possible to merge the scientific with the energetic. For the equivalent in Western herbalism ie. merging of Eastern and Western use of herbs, readers should consult The Energetics of Western Herbs by Peter Holmes and Michael Tierra's Planetary Herbology.
To the scientist or pharmacist a plant’s constituents may compose of, to use the words of Simon Mills “a crude chemical brew”, so the search is always on for an identifiable “active principle” [Mills 1994]. Herbalists on the other hand aim at a holistic approach which values the sum of the constituents - even those considered by pharmacists to be worthless. Many of the studies referred to in this book are based on this reductionist approach to research, however this does not necessarily devalue the results of this research, since isolation and experimentation with single constituents can provide information that can be adapted to a more holistic understanding of a herbs action. Knowledge of individual constituents is also essential for developing quality control methods, extraction procedures, understanding of pharmacological activity and pharmacokinetics [Bruneton 19951. It is not merely a necessary step in the isolation and synthesis of plant derived drugs.
It does not require a science degree to gain an understanding of the fundamental chemical structures found in medicinal herbs, but some knowledge of organic chemistry is desirable. The most user-friendly text for explaining the chemistry of herbs is Terry Willard's Textbook of Advanced Herbology, while Varro Tyler’s Pharmacognosy is an essential reference. Regularly browsing through peer review journals such as Phytochemistry and Tetrahedon Letters (available in university libraries) also provides good educational value.
Primary and secondary metabolites
Primary plant compounds are of universal occurrence ie. they are found in all or most plant species. They are products of vital metabolic pathways especially the citric acid/ krebs cycle and include proteins, fats, sugars, organic acids. The energy released by glycolysis of carbohydrates and through the citric acid cycle fuels the synthesis of all organic plant compounds or phytochemicals, including the secondary metabolites [Samuelsson 1992].
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