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Phytochemistry - An Introduction to Plant Chemistry
What Is Phytochemistry?
Phytochemistry is the name given to the study of the chemistry of plants.
Like animals, plants produce a wide variety of chemical compounds, called metabolites, as part of their normal life processes. These compounds perform different functions. For example, some enable plants to store energy in the form of sugar, whilst others are protective against disease or predators.
Primary and Secondary Metabolites
Primary metabolites include compounds such as carbohydrates and lipids - substances essential to the structure and life of the plant, as well as essential for human nutrition.
Carbohydrates are largely made up of sugars - saccharides. Glucose and fructose are examples of monosaccharides - they consist of a single saccharide molecule. Polysaccharides consist of several saccharide molcules linked together.
Lipids - commonly known as fats - provide a reservoir of fuel for cells. They also form a mjor compnent of cell membranes in both plants and animals.
A group of lipids known as fatty acids are important for human health. There are some fatty acids that the body cannot produce, and which must be sourced through the diet. These are know as essential fatty acids. The omega-3 and omega-6 fats are two well known essential fatty acids.
Using the primary metabolites, plants produce secondary metabolites, which are largely responsible for the plant's individual properties such as aroma, flavour, colour and medicinal actions. Secondary metabolites include terpenes, polyphenols, alkaloids and some glycodsides. The medicinal actions of herbs are largely due to these groups of chemicals.
Secondary metabolites include antioxidants, which defend the body against the effects of reactive free radicals. A large group of secondary metabolites known as terpenes provide us with many medicinal compounds, such as anti-inflammatory agents, expectorants and sedatives. The carotenoids - precursors of vitamin A - belong to the terpene group of compounds. Flavonoids - an important sub group of polyphenols - contain a number of important antioxidant compounds. In addition, certain of them are know to protect against heart disease and cancer. Plants rich in isoflavones, such as soy, exhibit marked hormone-balancing activity. The alkaloid group of secondary metabolites include caffeine ( a stimulant ) and ephedrine ( a decongestant ). Many alkaloids, such as mescaline and cociane, have hallucinogenic effects. Glycosides are a diverse group of chemicals particularly important in the study of herbal medicine. Cardiac glycosides improve the efficiency of the heart without increasing its need for oxygen. Cyanogenic glycosides produce the deadly poison cyanide. Indole-3-carbinol, which may help prevent colon and breast cancer, is produced in the body as it breaks down a glucosinolate found in cruciferous vegetables such as cabbage, broccoli and kale.
Many herbal actions can be described in a similar fashion to those of modern pharmaceuticals, including antispasmodic (muscle-relaxing) effects, analgesic (pain-relieving) effects and anti-inflammatory effects. Others are described according to terminology unique to herbal medicine, such as adapto-gens (herbs that help the body defend against physical stress), alteratives (herbs that slowly restore efficient body function), and carminatives (herbs that enhance digestion).
Herbs also often seem to affect one part of the body more than the others - what herb researchers call the herbs "affinity". For example corn silk (Zea mays) is one example that provides comfort for the urinary tract, while marsh mallow root (Althaea offidnalis) soothes the digestive tract.
In addition, whilst many herbs can be considered specific for a particular condition, most herbs actually have a variety of effects, known as primary and secondary actions. Chamomile, for example, soothes the digestive system and so is considered specific for treating stomach ulcers. However, it also has a calming effect on the nervous system, soothing frazzled nerves and relaxing tense muscles, as well as providing an effective topical treatment for certain skin conditions.
Tonics and Effectors
Herbal actions can be broadly categorised into two main groups - tonics and effectors. Tonics act to gently correct imbalance within certain body systems, and can be taken as a prevetative medicine. Effectors have a more immdediate action and are used to treat more acute and more specific symptoms and ailments.
Below is a list of common herbal actions.
Adaptogens are compounds in herbs which help the body cope with physcial stress, such as exposure to extreme cold or prolonged sleep deprivation. The mechanism of action is not yet understood but may work by affecting the release and action of stress hormones and blood glucose levels. Examples of adatogens include ginseng (Panax spp.) and the reishi mushroom (Ganoderma lucidem) .
Alteratives are herbs which work over time to restore body function. Some, such as burdock and nettle, seem to improve the efficiency of fundamental bodily functions such as digestion and excretion, whilst others, such as echinacea, act to boost the imuune system.
Anticatarrhal herbs are used to treat excess mucous. Many contain astringent tannins or volatile oils. Examples include echinacea and hyssop.
Anti-inflammatory herbs act to reduce the symptoms of inflammation such as redness and swelling. Topical agents include St. John's wort, whilst Devil's claw is an effective internal antiinflammatory.
Antimicrobial herbs contain compounds which kill pathogens such as bacteria, viruses and fungi. Echinacea has well known anti-microbial action, and also boosts the immune system. Cranberry is effective in the treatment of urinary tract infections. More about antimicrobial herbs.
Antioxidants are compounds that neutralise destructive molecules know as free radicals. free radicals are believed to be involved in the many degenerative diseases. More about antioxidants
Antispasmodic herbs relax the muscles, relieving muscle spams and easing muscle cramps. Some herbs act throughout the body, others have a more marked effect on specific systems. Many pf these herbs are also nervines, acting to relieve nervous tension as well. Examples of antispasmodics include valerian, which acts throughout the body, and chamomile, known for its effect on the digestive system.
Astringent herbs generally owe their action to a high content of tannins which helps to tighten and tone tissues, and to dry up excess secretions. They can be taken to treat internal ailments such as diarrhoea. or used topically eg. as a styptic to stop bleeding.
Carminative herbs stimulate digestion, and promote peristalsis - the movement of food through the digestive tract. Many herbs used in cooking are carminative herbs, such as thyme and ginger.
Cholagogue herbs stimulate the production of bile, an important component of the digestive process. Examples include barberry and dandelion root.
Demulcent herbs act to protect inflamed, irritated tissue, and are often targeted to specific body systems. Examples include marshmallow leaf, a urinary tract demulcent, and liquorice, a digestive tract demulcent.
Daiphoretic herbs induce perspiration and stimulate the circulation. They are commonly used to treat a fever. Examples include yarrow and ginger.
Diuretic herbs stimulate the production of urine, and so help to rid the body of excess fluid. Examples include dandelion and parsley.
Emmenogogue herbs provide benefit to the female reproductive system. Yarrow is believed to improve sluggish menstural flow. Others, such as black cohosh, act to normlase the function of the reproductive system.
Expectorant herbs promote the elimination of excess mucous from the lungs. The term is also sometimes used for other beneficial respiratory herbs, for example, relaxing expectorants such as liquorice soothe bronchial spasms and dry coughs. Stimulating expectorants eg. horehound, help the lungs expel mucous.
Galactogogue herbs are used by breastfeeding mothers to stimulate the flow of milk. Galactogogues include dill and fennel, both popular remedies for infant colic.
Hepatic herbs, such as milk thistle and barberry, assist in improving liver function.
Hypnotic herbs induce sleep and are used to treat insomnia. Examples include valerian and passionflower.
Hypotensive herbs help lower blood pressure. These include garlic and hawthorn.
Immunomodulator herbs stimulate the immune function. Among these herbs are echinacea, astragalus and the shiitake mushroom and reishi mushroom.
Laxative herbs treat constipation by stimulating the action of the bowels. Bulk-forming laxatives, such as psyllium and flaxseed, are high in fibre. Stimulant laxatives, such as senna and buckthorn, chemically induce peristalsis, the muscle activity that moves food through the digestive system.
Nervine herbs affect the function of the nervous system. Nervines may be relaxing, tonic or stimulating. Relaxing nervines include valerian and passionflower and St. John's wort. Herbs that stimulate the activity of the nervous system include caffeine-containing plants such as tea, guarana and peppermint.
Rubefacients are used topically to draw blood to an area for a localized warming effect. Some examples include ginger, black mustard and cayenne.
Vasodilator herbs cause dilation of blood vessels, useful in the treatment of cardiovascular conditions such as high blood pressure. Examples include ginkgo biloba and ephedra.
Vulnerary herbs, such as aloe and calendula, speed the healing of wounds. Vulnerary herbs may also be used internally.
St John's wort