Science Fair Project Encyclopedia
About 20 species, including:
Digitalis is a genus of about 20 species of herbaceous biennials, perennials and shrubs that was traditionally placed in the figwort family Scrophulariaceae. Due to new genetic research, it has now been placed in the much enlarged family Plantaginaceae.
The members of this genus are known in English as foxgloves. They are native to Europe, northwest Africa and west and central Asia. The scientific name means "finger", and refers to the ease which a flower of Digitalis purpurea can be fitted over a human fingertip. "Foxglove" has a similar origin, seen as a suitable glove for a fox paw.
The flowers are produced on a tall spike, are tubular, and vary in colour with species, from purple to pink, white and yellow.
The best-known species is the Common Foxglove , Digitalis purpurea. It is a biennial, often grown as an ornamental plant due to its violet flowers. The first year of growth produces only the long, basal leaves, while in the second year the erect leafy stem 0.5-2.5 m tall develops.
The use of Digitalis purpurea extract containing cardiac glycosides for the treatment of heart conditions was first described by William Withering. In contemporary medicine, a purer form of digitalis is used to strengthen cardiac contractility and as an antiarrhythmic agent to regulate heart rhythm. It is therefore often prescribed for patients in heart failure.
A group of pharmacologically active compounds are extracted mostly from the leaves of the second year's growth, and in pure form are referred to by common chemical names such as digitoxin or digoxin, or by brand names such as Lanoxin, or Purgoxin.
Digitalis works by inhibiting sodium-potassium ATPase, which increases intracellular calcium. The increased intracellular calcium gives a positive inotropic effect. It also has a vagal effect on the parasympathetic nervous system, and as such is used in reentrant cardiac arrhythmias and to slow the ventricular rate during atrial fibrillation. The dependence on the vagal effect means that digitalis is not effective when a patient has a high sympathetic nervous system drive, which is the case with acutely ill persons.
Digitalis toxicity (Digitalis intoxication) results from an overdose of digitalis and can result in jaundiced (yellow) vision and the appearance of blurred outlines (halos), as well as bradycardia in extreme cases. Because a frequent side effect of digitalis is reduction of appetite, some individuals have abused the drug as a weight loss aid.
Digitalis is a classic example of a drug derived from a plant formerly used by folklorists and herbalists: herbalists have largely abandoned its use because of its narrow therapeutic index and the difficulty of determining the amount of active drug in herbal preparations. Once the usefulness of digitalis in regulating pulse was understood, it was employed for a variety of purposes, including the treatment of epilepsy and other seizure disorders, now considered inappropriate.
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