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The
medicinal effects of certain plants are well known.
Senna, for example, has been taken as a laxative
for thousands of years, and aloe vera was known
to Cleopatra as a soothing skin remedy. It is
only recently, however, that the active constituents
responsible for the medicinal actions of plants
have been isolated and observed. Knowing a little
about the chemicals contained in plants helps
you understand how they work within the body.
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Mucilage
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Found
in many plants, mucilage is made up of polysaccharides
(large sugar molecules) that soak up water, producing
a sticky jellylike mass. Mucilage lines the mucous
membranes of the digestive tract, protecting against
irritation, acidity and inflammation. This soothing
and protective action appears to extend to other
areas, including the mucous membranes of the throat,
lungs, kidneys, and urinary tubules. Slippery
elm (Ulmus rubra) is a typical mucilaginous herb. |
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Phenols
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This
group of compounds includes salicylic acid - the
natural forerunner of aspirin. Salicylic acid
is found in many plants, for example wintergreen
(Gaultheria procumbens) and white willow (Salix
alba). Another phenol is thymol - a constituent
of thyme (Thymus vulgaris). Phenols are antiseptic
and reduce inflammation when taken internally,
yet they have an irritant effect when applied
to the skin. |
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Tannins
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Tannins
are produced to a greater or lesser degree by
all plants. The harsh, astringent taste of tannin-laden
bark and leaves makes them unpalatable to insects
and grazing animals. Tannins contract the tissues
of the body - hence their use to "tan"
leather.
They draw the tissues closer together and improve
their resistance to infection. Oak bark (Quercus
robur) and black catechu (Acacia catechu) are
both high in tannins. |
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Coumarins
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Coumarins
of different kinds are found in many plant species
and have widely divergent actions. The coumarins
in melilot (Melilotus officinalis) thin the blood,
bergapten, found in celery (Apium graveolens),
is used as a sunscreen, and khellin, found in
visnaga (Ammi visnaga), is a powerful smooth muscle
relaxant. |
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Anthraquinones
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Anthraquinones
are the main active constituents in herbs such
as senna (Cassia senna) and Chinese rhubarb (Rheum
palmatum), both of which are taken to relieve
constipation. Anthraquinones have an irritant
laxative effect on the large intestine, causing
contractions of the intestinal walls and stimulating
a bowel movement approximately 10 hours after
being taken. They also make the stool more liquid,
easing bowel movements. |
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