Herbs contain a vast
range of chemicals, ranging from water and inorganic salts, sugars and
carbohydrates to highly complex proteins and alkaloids.
Plant acids
Weak organic acids
are found throughout the plant kingdom. A typical example is the citric acid
found in lemons.
The organic acids
can be divided into those based on a carbon chain, and those containing a
carbon ring in their structure, but they all have a -COOH group in common.
The chain acids (or
aliphatic acids) range from the simple formic acid we can feel in the sting of
nettles to the more complex ones like citric acid and valeric acid, the latter
being the basis for a sedative used in allopathic medicine.
The ring acids
(aromatic acids) are an important pharmacological group. The simplest aromatic
acid, benzoic acid, can be found in many resins and balsams like gum benzoin,
tolu, Peru balsam and also in cranberries. It can be used as a lotion or an
ointment, can be a beneficial inhalant for chronic bronchial problems, and has
antiseptic, anti-pyretic and diuretic actions.
Alcohols
Alcohols are found
in various forms in plants, often as constituents of volatile oils or as
sterols, like the alcohol oil geraniol in attar of rose and menthol in
peppermint oil. Other common forms of alcohol are waxes, combinations of
alcohols and fatty acids, which are found in plants in the coating of leaves
and in other parts. The commonly used carnauba wax for instance is obtained
from the palm Copernicia cerifera.
Volatile oils
Most of the volatile
oils are based on simple molecules like isoprene or isopentane, which can
combine in many different ways to form terpenes, containing multiples of the
basic 5-carbon molecules, sometimes with slight variations, making up the
volatile oils.
We can find the
volatile oils in the aromatic plants, such as peppermint or thyme, where
different oils-sometimes up to 50 or more-combine to give the plant its
particular smell. Depending on the combination of oils the smell will vary and
even be slightly different within the same species, depending on the
concentrations of oils.
By extracting these
oils, the so-called essential or aromatic oils are produced, which can be used
therapeutically, but which also are used to a large extent for the production
of perfumes.
The range of
aromatic oils is very large and they each have unique properties, but they also
share some common actions worth mentioning.
All aromatic oils
are antiseptics, good examples being eucalyptus oil, garlic oil and thyme oil.
As the oils are very easily transported and distributed throughout the body,
they act both locally and on the whole system. When they are taken internally
or applied externally, they will soon show up in the urinary system, the lungs
and the bronchiaIs, and in secretions like sweat, saliva, tears or the vaginal
fluids. They can even occur in mother's milk or travel through the placenta
into the fetus. Besides their direct antiseptic action they also stimulate the
production of white blood-cells, thereby augmenting the body's own natural
defense system.
The volatile oils
stimulate the tissue they come in contact with, either leading to slight
'irritations' (as in the case of mustard oil) or to a numbing (as with menthol
and camphor). They aid digestion by stimulating the lining of the colon, which
sets off a reflex that increases the flow of gastric juices and induces a
feeling of hunger. Also they can help to ease griping pains by relaxing the
peristalsis in the lower part of the intestines.
The volatile oils
also act on the central nervous system. Some will relax and sedate, like
chamomile, others will stimulate, like peppermint, and all tend to induce a
state of inner ease and well-being, thus reducing tension and depression. When
aromatic oils are applied externally, part of their effect is due to their
actions on the nose, as the olfactory nerves transmit the smell to the brain
and trigger off a reaction there.
As volatile oils
evaporate very easily, herbs containing these oils have to be stored carefully
in well sealed containers.
Carbohydrates
A great variety of
carbohydrates can be found in plants, either in the form of sugars such as
glucose and fructose, or as starches, where they serve as the main energy
store. They can also be in the more complex form of cellulose, which gives
structural support to plants.
The large
polysaccharides, like cellulose, can further bond with other chemicals and
produce molecules like pectin, found for instance in apples, or seaweed gums
like algin, agar or carragum, found in Irish moss. They are all very viscous
and demulcent and are used to produce gels that are utilized in medicine and in
food preparations.
Gums and mucilages,
which are very complex carbohydrates, are contained in some excellent soothing
and healing herbs, like the demulcents coltsfoot, plantain and marshmallow.
Their action relaxes the lining of the gut, triggering a reflex that runs
through the spinal nerves to areas related embryologically, like the lungs and
the urinary system. In this way the mucilages work in a twofold manner: they
reduce irritation and inflammation in the whole of the alimentary canal, reduce
the sensitivity to gastric acid, prevent diarrhea and reduce the peristalsis;
they also work via a reflex on the respiratory system, reducing tension and
coughing and increasing the secretion of watery mucus.
Phenolic compounds
Phenol is a basic
building block of many important plant constituents. Phenolic compounds may be
simple in structure, or a complex combination of a range of basic molecules. One
of the simple phenolics is salicylic acid, which is found often in combination
with sugar, forming a glycoside, as in willow, cramp bark, wintergreen and
meadowsweet. This chemical has antiseptic, pain killing and anti-inflammatory
properties, and is used by allopathic medicine in the form of acetylsalicylic
acid, better known as aspirin.
Eugenol, the
pain-killing oil found in cloves, and thymol from oil of thyme both have
similar effects to salicylic acid. Part of the antiseptic action of bearberry
on the urinary system can be explained by the presence of the phenol
hydroquinone.
Tannins
Tannins in herbs cause
an astringent action. They act on proteins and some other chemicals and form a
protective layer on the skin and the mucous membranes. Thus they can for
instance bind the tissue of the gut and reduce diarrhea or internal bleeding.
Externally they are useful in the treatment of burns, for sealing wounds and to
reduce inflammation. Tannins help in infections of the eye (conjunctivitis),
mouth, vagina, cervix and rectum.
Coumarins
The highly evocative
smell of new mown hay has its basis in the coumarin group of chemicals. It is,
of course, not just grass that contains these beautifully aromatic
constituents; sweet woodruff is another example. Coumarin itself has limited
effects on the body, but one of its metabolites, di-coumarol, is a powerful
anti-clotting agent. Allopathic medicine has used the coumarins as a basis for
warfarin, an anticlotting drug used as a guard against thrombosis in small dosage
and as a rat poison in large doses.
Anthraquinones
Plants containing
anthraquinones are known to be effective purgatives and they also happen to be
good natural dyes. They appear usually in the form of glycosides (in a chemical
combination with a sugar) and are found for instance in rhubarb, yellow dock,
senna, buckthorn and aloe. They work by gently stimulating the colon after
about 8-12 hours of ingestion by stimulating the peristalsis of the intestines,
but they can do this only when natural bile is present. As there may be a
tendency to colic pains through an over-stimulation of the colon wall, they are
often given in combination with carminative herbs.
Flavones and flavonoid
glycosides
One of the most common
groups of plant constituents in herbs are the flavones and the flavonoid
glycosides. They are known to have a wide range of activities, from
anti-spasmodic and diuretic to circulatory and cardiac stimulants. Some, for
instance, like rutin, hesperidin and the bio-flavonoid vitamin P, reduce permeability
and fragility of the capillaries and so help the body to strengthen the
circulatory system and to lower the blood pressure. Buckwheat is a good example
of a useful herb for such problems. The bio-flavonoids are also essential for
the complete absorption of vitamin C and occur in nature wherever vitamin C is
present. Anther flavonoid, present in milk thistle, is responsible for its
action in aiding the liver.
Saponins
The saponins have
attracted the attention of pharmaceutical chemists as they can be used in the
synthesis of cortisone-a strong anti-inflammatory drug-and in the synthesis of
sex hormones. While the saponins contained in herbs do not directly act in the
same way, the body can use them as raw materials to build up appropriate
chemicals. To show the similarity between a natural saponin and the more potent
synthesized drugs, we can compare cortisone with diosgenin from wild yam and
see that they are very similar.
Typical
anti-inflammatory herbs that contain saponins include golden rod, chickweed,
figwort and wild yam.
Another important
action of saponins is their expectorant action through the stimulation of a
reflex of the upper digestive tract, which occurs in remedies such as primrose,
mullein, violet and daisy.
Cardiac glycosides
Very similar to the
saponins are the cardiac glycosides. These have been the object of intensive
investigation ever since they were discovered in 1785 in foxglove, when it was
recognized by medicine that these glycosides can support the failing heart.
The cardiac glycosides
are formed by a combination of a sugar and a steroidal agylcone. The main
activity is defined by the shape and structure of the agylcone, but it is the
sugar that determines the bioavailability of the active agylcone.
Many flowering plants contain
cardiac glycosides. The best known sources are foxglove, lily of the valley,
squill and the Strophanthus family. In herbal medicine, lily of the valley is
preferred over foxglove, as foxglove is potentially poisonous, whereas lily of
the valley, quite as effective, does not lead to a build-up of toxic components
in the body.
Therapeutically, the
cardiac glycosides have the incredible ability to increase the force and power
of the heart-beat without increasing the amount of oxygen needed by the heart
muscle. They can thus increase the efficiency of the heart and at the same time
steady excess heart-beats without strain to the organ.
Bitter principles
The bitter principles
represent a grouping of chemicals that have an exceedingly bitter taste. Chemically
they show a wide diversity of structure, with most bitters belonging to the
iridoids, some to the terpenes and some to other groups.
The bitter principles
have been shown to have valuable therapeutic effects. Through a reflex action
via the taste buds, they stimulate the secretion of all the digestive juices
and also stimulate the activity of the liver, aiding hepatic elimination.
Research from China suggests that the bitter principle in Gossypium spp. may
have a role as a male contraceptive by reducing the level of sperm production.
The property of
bitterness imparted to plants by these principles is usually part of the
overall activity of the herb, and we find sedatives such as hops and valerian,
cough remedies like white horehound, anti-inflammatory such as bogbean and
devil's claw, and the vulnerary marigold all sharing this valuable action.
Alkaloids
The alkaloids are
perhaps the most potent group of plant constituents that act upon the human
body and mind. They include the hallucinogen mescaline at one extreme and the
deadly poison brucine at the other. There are alkaloids that act on the liver,
the nerves, the lungs, and the digestive system. Many of the most valued herbs
contain these potent chemicals. However, within the plants themselves there
appears to be no important function for them, apart from possibly being a store
for excess nitrogen.
The alkaloids as a group are very diverse in structure. They
have nitrogen in their structure and all have a marked physiological activity.
Chemically they are divided into thirteen groups based upon their structure.
(source unknown)
